A car has been driven into pedestrians outside a major train station in Australia in what police have called "a deliberate act".
Up to 14 people have been injured, several critically, outside Flinders Street station in Melbourne.
Police have arrested the driver of the white Suzuki SUV and another man who was in the vehicle.
"We believe based on what we have seen that it is a deliberate act," Victorian Police commander Russell Barrett said. "The motivations are unknown."
The Victoria State ambulance service said it had taken 13 people to hospital, including a pre-school child with a serious head injury.
Police said the motive for the incident was not known, but it had chilling echoes of several attacks by Islamist militants in various parts of the world over the past few years.
In January, four people were killed and more than 20 injured when a man deliberately drove into pedestrians at a spot just a few hundred metres away from Thursday's incident, though that was not terrorism-related.
Prime Minister Malcolm Turnbull said federal and state police as well as security agencies were working together to secure the scene and investigate the "shocking incident".
"Our thoughts and prayers are with the victims and the emergency and health workers who are treating them," Mr Turnbull said in a post on his official Twitter account.
Daniel Andrews, premier of the state of Victoria, of which Melbourne is the capital, described it as a "horrible incident."
He added: "Stay safe. Check on your loved ones. And thank you to our brave emergency services."
A statement issued by the City of Melbourne local authority said: "At this stage, the details of this incident are not fully known.
"What is known is this: a vehicle has struck and injured pedestrians at the corner of Elizabeth and Flinders streets. Victoria Police have two people in custody.
"Our emergency services, including Victoria Police, have control of this situation. We have every confidence in them to protect Melbourne in such horrific circumstances.
"We have the best advice available to us and we will continue to work with the State Government and Victoria Police to keep people safe.
"At this time our thoughts are with those most affected and of course we will work with agencies to provide immediate and long-term support to them."
Australia has been on a "high" national threat level since 2015, citing the likelihood of attacks by Australians radicalised in Iraq and Syria.
A staunch ally of the United States and its campaign against Isis in Syria and Iraq, Australia believes more than 100 of its citizens are fighting there.
Additional reporting by agencies
