Australia, United States begin their biggest joint military exercise

USS Bonhomme Richard amphibious assault ship Executive Officer Rich Lebron (2nd R) speaks to Australian journalists in the Pacific Ocean off the coast of Sydney, Australia, before a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia June 29, 2017. REUTERS/Jason Reed

SYDNEY (Reuters) - Australia and the United States began their biggest ever joint military exercises on Thursday, a show of force, largely at sea, aimed at sending a message both to allies and potential foes, including China.

The exercises involving 33,000 U.S. and Australian troops on board battleships equipped with strike jets, comes as tension over China's more assertive activity, particularly in the disputed South China Sea, has raised fears of confrontation.

A U.S. Navy Landing Craft Air Cushion (LCAC) appears from the stern of the USS Bonhomme Richard amphibious assault ship during events marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, off the coast of Sydney, Australia July 29, 2017. REUTERS/Jason Reed

Admiral Harry Harris, head of the U.S. Pacific Command, asked how he thought China would view the exercises, said the size of the deployment was intended as a signal.

"I'm pleased about that message it sends our friends, allies, partners and potential adversaries," Harris told reporters on board the USS Bonhomme Richard.

Relations between the United States and China have soured in recent months as the United States seeks to counter what it perceives as Chinese assertiveness in the Pacific, encapsulated by Beijing's artificial island building in the South China Sea.

A U.S. Navy Landing Craft Air Cushion (LCAC) heads across the Pacific Ocean towards Sydney, Australia, during events marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, July 29, 2017. REUTERS/Jason Reed

China claims most of the resource-rich South China Sea, through which about $5 trillion in ship-borne trade passes every year. Brunei, Malaysia, the Philippines, Vietnam and Taiwan also have claims on the waterway.

The United States estimates China has added more than 3,200 acres (1,300 hectares) of land on seven reefs and tiny isles in the South China Sea over the past three years, installing runways, ports, aircraft hangars and communications equipment.

James Curran, professor of politics and foreign policy at the University of Sydney, said the exercise illustrated the close military ties between the United States and Australia but could raise worry in China about being surrounded.

U.S. Marine MV-22B Osprey aircraft land on the deck of the USS Bonhomme Richard amphibious assault ship during events marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

"When there are concerns about China's activities in the South China Sea, this military exercise will send a signal and take on greater significance," Curran said.

"China will be concerned if it looks like containment, when you have Australia, the United States and others trying to gang-up on China."

The exercise will go on for a month in Australian territorial waters and will include training in land and air operations.

A flag party of U.S. Marines and Navy personnel take part in a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia aboard the USS Bonhomme Richard amphibious assault ship on the the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

(Reporting by Colin Packham; Editing by Robert Birsel)

U.S. Navy Admiral Harry Harris, Commander of the U.S. Pacific Command, salutes at a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, aboard the USS Bonhomme Richard amphibious assault ship in the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

U.S. Navy Admiral Harry Harris, Commander of the U.S. Pacific Command, and Australian Navy Vice Admiral David Johnston unfurl the flag for Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, aboard the USS Bonhomme Richard amphibious assault ship in the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

U.S. Marines aboard the USS Bonhomme Richard amphibious assault ship stand in formation during a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia aboard the USS Bonhomme Richard amphibious assault ship on the the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

U.S. Marines aboard the USS Bonhomme Richard amphibious assault ship stand in formation during a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia aboard the USS Bonhomme Richard amphibious assault ship on the the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

U.S. Marines stand aboard the USS Bonhomme Richard amphibious assault ship during a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia on the the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

A member of the Australian Army sits in the audience alongside a U.S. flag as the backdrop of a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, aboard the USS Bonhomme Richard amphibious assault ship on the the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

A crewman aboard a U.S. Marine MV-22B Osprey Aircraft looks out as it lifts off the deck of the USS Bonhomme Richard amphibious assault ship off the coast of Sydney, Australia, after a ceremony on board the ship marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, June 29, 2017. REUTERS/Jason Reed

The USS Bonhomme Richard amphibious assault ship sails in the Pacific Ocean off the coast of Sydney, Australia, after a ceremony on board the ship marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, June 29, 2017. REUTERS/Jason Reed

Participants in a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, board a U.S. Marines MV-22B Osprey Aircraft on the deck of the USS Bonhomme Richard amphibious assault ship off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

U.S. Navy Admiral Harry Harris (L), Commander of the U.S. Pacific Command, shakes hands with Australian Minister for Urban Infrastructure Paul Fletcher during a ceremony for Talisman Saber 2017, a biennial joint military exercise between the United States and Australia aboard the USS Bonhomme Richard amphibious assault ship in the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

Participants in a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia, arrive on a U.S. Marines MV-22B Osprey Aircraft on the deck of the USS Bonhomme Richard amphibious assault ship off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

U.S. Marines aboard the USS Bonhomme Richard amphibious assault ship stand in formation during a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia aboard the USS Bonhomme Richard amphibious assault ship on the the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

A crewman aboard a U.S. Marines MV-22B Osprey Aircraft looks out over the deck of the USS Bonhomme Richard amphibious assault ship before landing on it off the coast of Sydney, Australia, at the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia June 29, 2017. REUTERS/Jason Reed

A crewman aboard the USS Bonhomme Richard amphibious assault ship guides the press off a U.S. Marines MV-22B Osprey Aircraft before a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia off the coast of Sydney, Australia, June 29, 2017. REUTERS/Jason Reed

Journalists record activities aboard the USS Bonhomme Richard amphibious assault ship off the coast of Sydney, Australia, before a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia June 29, 2017. REUTERS/Jason Reed

(L-R) U.S. Navy Rear Admiral Marc Dalton, Commander of the U.S. Pacific Command Admiral Harry Harris and Australian Minister for Urban Infrastructure Paul Fletcher participate in a ceremony marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia aboard the USS Bonhomme Richard amphibious assault ship in the Pacific Ocean off the coast of Sydney, Australia, June 29, 2017.REUTERS/Jason Reed

The USS Bonhomme Richard amphibious assault ship manoeuvres into port in front of the Sydney Opera House in Australia, June 29, 2017 after a ceremony on board the ship marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia. REUTERS/David Gray

The USS Bonhomme Richard amphibious assault ship manoeuvres into port in front of the Sydney Harbour Bridge in Australia, June 29, 2017 after a ceremony on board the ship marking the start of Talisman Saber 2017, a biennial joint military exercise between the United States and Australia. REUTERS/David Gray