British police say they are responding to a series of major incidents in London including a van veering off London Bridge and striking pedestrians and a knife attack at nearby Borough Market.
The Metropolitan Police say they are also responding to an incident at Vauxhall.
British transport police say there are multiple casualties.
The attacks happened on a busy Saturday night at about 10pm as central London was crowded with people.
The first attack involved a van mowing down pedestrians on London Bridge.
A witness told the BBC she saw a speeding white van veering into pedestrians. The witness said the van hit five to six people.
Reuters television pictures showed dozens of emergency vehicles in the area around London Bridge.
London's transport authority said London Bridge rail station had been closed at the request of the police.
One witness told Reuters that she saw what appeared to be three people with knife wounds and possibly their throats cut.
British Prime Minister Theresa May said she is “in contact with officials and is being regularly updated on the incident at London Bridge”.
Speaking to Sky News, Foreign Minister Julie Bishop said there are no reports of Australians being caught up in the incident so far.
“We are following the media reporting on this. It is still unfolding,” Ms Bishop said.
“So far we have had no reports of any Australians involved. It is too early to say this is a terror incident, but although we have seen this before.
“Certainly we are all on edge given what has happen in Manchester recently.”
On May 22, a suicide bomber killed 22 people at a pop concert by US singer Ariana Grande in Manchester in northern England.
The Manchester bombing was the deadliest attack in Britain since July 2005, when four British Muslim suicide bombers killed 52 people in coordinated attacks on London's transport network.
