This morning, several explosions were reported on buses and on Underground trains and stations. The number of bombings is now thought to be four. The bus destroyed at Tavistock Square may have been attacked by a suicide bomber. At least one, perhaps two, unexploded devices have been found at other Underground locations.
The BBC put the number of dead at 39 on the news a few minutes ago. Around 700 have been injured. Unofficial estimates put the number of dead as high as 50. A BBC report from an hour ago said that 35 were killed in the Underground bombings, and two on board the bus at Tavistock Square.
There were attacks in four locations: between Aldgate East and Liverpool Street tube stations; between Russell Square and King's Cross tube stations; at Edgware Road tube station; and on a bus at Tavistock Square.
UPDATED - 20:40 GMT, July 7th.
At around 11:30AM, an un-named Government source put the number of dead at 20. Simon has posted below that CNBC is reporting 50 killed at Euston Station alone - this report seems to have been incorrect.
A spokesman for the ambulance service said emergency services had been called to seven locations - not including Euston Station - and could confirm a bus had been bombed at Taverstock Square. Police reports of three bus bombings appear to have been mistaken.
The London mobile phone network has been shut down. The landlines are under immense pressure, so do not panic because you cannot reach friends or loved ones. Both the Underground and London bus services have been closed. Soldiers have deployed at various points within the city.
AP reported that a senior Israeli official says Israel was told by Scotland Yard, minutes before bombings, they were expecting a terrorist attack. The Israelis are strongly denying the report, as are the Metropolitan police.
Prime Minister Blair is leaving the G8 summit to meet with ministers and be briefed by the commanders of the emergency services. He said the explosions appear to be a series of terrorist attacks, and reiterates his committment to defeat terrorism.
6:43PM GMT (JK): Death toll now confirmed at 37, expected to continue rising. Normblog has details, and his post also has links to pictures.
7:20PM GMT (JK): CNN appears to have discovered that bombing buses crerates horrific injuries, even among the survivors. They're covering this in deail, and asking questions like how one identifies the bodies (one-word answer: ZAKA - bet they'll be called in). Amazing what happens when Jews aren't the ones riding the bus.
(Information is reaching the TV news long before it reaches online news sources. I'll be liveblogging news as I get it. Please post news on the attacks in the comments box. See also Bill Roggio's analysis, London Falling, and The London 7/7 Hunt Begins)