British police are responding to three emergency incidents in London on Saturday night - one on London Bridge involving a van, a knife attack at Borough Market and a third in Vauxhall.
Police have issued security advice on Twitter to Londoners saying to "run, hide tell" if caught in an attack.
British Transport Police says there are multiple casualties.
The attacks happened on a busy Saturday night at about 10pm as in popular areas, crowded with people.
Britain's Press Association news agency says members of the public were told to run away as fast as they could from London Bridge area, which is filled with restaurants and pubs.
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.
