New Zealand is ringing in 2020 and welcoming a new decade with fireworks and huge celebrations in Auckland and Wellington.
The clock struck midnight an hour after Samoa and Christmas Island, which were the first countries to enter the new decade.
At 1pm UK time, 2020 will arrive in eastern parts of Australia, including Sydney, where a spectacular harbour fireworks show went ahead at 9pm local time and calls for the event to be scrapped.
The full fireworks will still go ahead at midnight (1pm UK time).
In the UK, London's show will feature 12,000 fireworks, including 2,000 fired from the London Eye on the River Thames, and Big Ben's chimes for the first time in a year amid renovation work.
Outlying American islands in the South Pacific, which are just east of the International Date Line, will be the last to welcome 2020 - at 12pm UK time on Wednesday, exactly 25 hours after Samoa.
In Wales, there will be a fireworks display at Winter Wonderland in front of City Hall at midnight.
It will be presented by James Williams from 11.30pm and he will be joined by a special guest and will introduce the evening firework display, which will start at midnight.
Hundreds are also expected to take part in the Nos Galan Road Race in Mountain Ash that will once again be started by a mystery runner.
Councillor Ann Crimmings says: ""Nos Galan captures the attention and admiration of the sporting world across the UK and further afield because it is such a unique event.
"With a great atmosphere, fireworks and funfair and the chance to see the celebrity Mystery Runner or Runners launch the proceedings, it's a great night out."
