Several people have been injured after explosions blamed on a power surge led to the whole London Underground network being closed down.
British Transport Police said some of the power surges had caused explosions.
Surges took place at Aldgate, Edgware Road, King's Cross, Old Street and Russell Square stations.
A spokesman said there were "walking wounded" at Liverpool Street station but one person's life was reported to be "at risk".
London Fire Brigade said four crews were at Liverpool Street and more were on their way.
A British Transport Police spokesman said that emergency services were dealing with reports of an explosion at 0849 BST on the Metropolitan Line between Liverpool Street and Aldgate.
One passenger, who had left the Tube at Fenchurch Street Station, and walked to Aldgate East, told BBC Five Live that he saw injured people.
"As I walked through the bus station I could see people lying on the ground, black, as if they'd been covered in smoke. There were about three or four people on the floor being treated."
Eyewitness Paul Woloszyn from BBC News, who was at Blackhorse Road station on the Victoria Line, said: ""We were told there was a bomb at Liverpool Street station.
"I was on the Tube, and they stopped the train and told everyone to get off an evacuated the station."
He said staff had said the entire Tube network had been affected, and leaflets had been handed out with details of alternative bus routes.
Another eyewitness, Dorothy Molloy, had been on a Tube train at King's Cross and said "staff just chucked everyone out of the station".
She said staff there had not given any details, but she said two passengers she had spoken to had said they had received messages saying there had been bombs.
"People didn't really know what was going on, they were just huffing and puffing and saying how annoying it was," she said.
"People don't seem to be panicked, but there's so many police and ambulances coming into the areas. People are just concerned, and some are just annoyed at the delay."
This damn country cat go ONE good day without something horrible happing
EBC: Northeners, Huh! What are they good for?! Absolutely nothing!
Cybertron, Justice league...MM, HAB SDN City Watch: Sergeant Detritus
Days Unstabbed, Unabused, Unassualted and Unwavedatwithabutchersknife: 0
Eyewitness Paul Woloszyn from BBC News, who was at Blackhorse Road station on the Victoria Line, said: ""We were told there was a bomb at Liverpool Street station.
Captain Tycho! The worst fucker ever!
The Best reciever ever!
Ah, just what I need to hear before going to work.... I, too, ride a commuter train although mine doesn't go underground.
I notice no one wants to say "terrorism", but all know that's on everyone's minds.... Just one explosion would indicate accident, but multiple ones are more suspicious.
Jason von Evil wrote:London has the power grid of a frickin Galaxy class. Seriously, how can a power surge destroy a double decker bus and inflict the other damage?
The news is a lot of 'sources say' and 'a caller said a friend of him saw', but considering "one caller to BBC Five said his friend had seen "the bus ripped open like a can of sardines and bodies everywhere." I doubt this is just some random accident.
If this is an Islamic terrorist related incident, and considering that it was only just announced today that London won the games......has Paris been put on alert yet?
Wow. This is one Hell of an incident. How could it get three buses and six stations without it being entirely intentional?
