The BBC News website is covering events as they unfold:
1055 A doctor tells Reuters there are at least 90 casualties at Aldgate station
1053 Home Secretary Charles Clarke makes a statement outside Downing Street about "dreadful incidents" causing "terrible injuries". He says Prime Minister Tony Blair has been informed and advises the public in London not to make unneccessary journeys
1049 Police say there are serious casualties, but no deaths are confirmed, Associated Press reports
1025 The BBC's Andrew Marr, with the prime minister in Gleneagles, says Number 10 is "still unsure" whether the explosions are a terrorist attack
1023 confirmed explosion on a bus in Tavistock Place
1021 Scotland Yard reports "multiple explosions" in London, the Press Association reports
1014 An eyewitness tells PA that a bus has been ripped apart in an explosion in central London
1009 Witness Christina Lawrence, who was on a train leaving Kings Cross, tells BBC News 24: "There was a loud bang in the tunnel and the train just stopped and all of a sudden it was filled with black, gassy smoke and we couldn't breathe"
1002 Scotland Yard says it is dealing with a "major incident"
0940 British Transport Police say power surge incidents have occurred on the Underground at Aldgate, Edgware Road, King's Cross, Old Street and Russell Square stations
0933London Underground reports "another incident at Edgware Road" station, PA reports
0933 Passengers are told that all London Underground services are being suspended because of a power fault across the network, PA reports
0924 British Transport Police say the incident was possibly caused by a collision between two trains, a power cut or a power cable exploding. Police report "walking wounded"
0915 Press Association reports emergency services called to London's Liverpool Street Station after reports of an explosion
0849 An incident on the Metropolitan Line between Liverpool Street and Aldgate is reported to British Transport Police