It's believed no Australians have been involved in a terror attack near London's Houses of Parliament that has left at least four people dead.
Foreign Minister Julie Bishop says that has been confirmed by Australia's High Commissioner in London, who she has been in contact with from Washington.
"I can assure Australians that to this point no Australians have been identified as being involved," she told reporters on Thursday.
Ms Bishop extended the Australian government's deepest sympathy to the people of the UK after speaking to her counterpart Boris Johnson.
The minister insisted the government is doing all it can to ensure Australia is safe from such an attack.
"But as we have seen in the United Kingdom today, these events can occur," she said.
Ms Bishop said that although nothing had been confirmed, the attack had the hallmarks of recent attacks by so-called Islamic State.
Opposition Leader Bill Shorten has pledged support to Britain after the attack.
"This shocking crime, designed to weaken the U.K., will only make her stronger. All Australians stand with Britain today," he tweeted early on Thursday.
The attacker, who was shot dead, mowed down several pedestrians on Westminster Bridge before crashing it then running through the gates of the Palace of Westminster and fatally stabbing a police officer.
Prime Minister Malcolm Turnbull said Australia's heartfelt sympathies were with the victims of the attack.
"Australia stands in resolute solidarity with the people of Britain in war against terrorism," he tweeted.
