More updates about the bus that "blew up" and strange, unconfirmed reports about the driver of the bus. Courtesy of Sky News.
BLAST 'RIPS BUS IN TWO'
One eyewitness described "half a bus flying through the air" shortly after an explosion tore apart a London bus.
Other witnesses and passengers described horrifying scenes in Tavistock Square.
The number 30 was travelling from Hackney to Marble Arch when at 9.50am a blast ripped through the bus.
It came just minutes after three explosions on the capital's Tube network.
One witness claimed that the bus driver had got out and asked for directions while another said he had ran away. Neither accounts are confirmed.
The roof of the bus was ripped off in the blast and sent hurtling several metres away while the back of the bus was torn off.
The roof was left lying on the road and the bus surrounded by debris.
The front of the British Medical Association building, near the bus blast, was splattered with blood to a height of around 15ft.
It is not known whether a bomb or a suicide bomber was behind the attack.
Cycle courier Andrew Childes, 36, from London was on his way to the British Medical Association's headquarters in Tavistock Square, Euston, when the bus blew up outside the building.
He said: "I heard a bang, a thudding deep sound. There was a big cloud of grey smoke. I was about 250 metres away at the time and I stopped dead in my tracks and didn't go any further. I waited for a bit and then went to see what had happened.
The bus was just splintered metal, and it was all bent over. The top part of the bus was completely exposed, as if the roof had been ripped off it. There was a bit of panic going on, a few screams and shouts, but there wasn't massive panic.
"I didn't see if anyone was on the bus or if anybody was hurt. Somebody told me they saw the driver running away from the bus but I don't know if that's true.
Another eyewitness to the explosion said he was blown off his feet as he was rocked by the blast. "I got off the Tube at King's Cross as I was told to and began walking into central London. As I was crossing the road, I didn't even see the bus, but was knocked off my feet. I looked up and could see people trying to climb down from the top of the bus."
Belinda Seabrook said: "I was on the bus in front and heard an incredible bang, I turned round and half the double-decker bus was in the air.
Mrs Seabrook said the bus was travelling from Euston to Russell Square and had been "packed" with people turned away from Tube stops.
"It was a massive explosion and there were papers and half a bus flying through the air, I think it was the number 205," she said.
"There must be a lot of people dead as all the buses were packed, they had been turning people away from the tube stops. We were about 20 metres away, that was all."
"I was on the bus. I looked round and the seats behind me were gone," another witness who was on one of the buses said.
Parking attendant Ade Soji, 35, of Dagenham, Essex, said he had to run for his life after the bus exploded.
He said: "I was helping a member of the public with directions when the bus stopped and the driver asked me the name of the street. I told him Tavistock Square and he called me over. Just as I was about to go, I heard the bus explode. In another second I would have been dead. I had to run for my life. I looked back and saw the roof flying over."
Paul Tripea, owner of the Russell Square Cafe, said people had rushed inside following the explosion.
"One of the security guards from a nearby hotel rushed in and said he saw the bus explode around Tavistock Square," said Mr Tripea.We have also heard that there is a suspect package in Russell Square."
Sky News journalist Bob Mills said: "The top of the bus had clearly been blown off and looking at the wreckage it looks as if the bomb or whatever it was placed at the back of the top deck. People were using tables from a nearby hotel as a stretcher."
Suzanne Flowerday, 16, who is doing work experience in Soho, said: "I just heard a bang and the roof and back of the bus came off.
"There was debris everywhere and people running around. There were police and fire brigade everywhere - everyone was distraught, no-one knows what is going on.
"It can't be a power surge if buses are blowing up as well. There was a woman who had cracked ribs and another lady, half of her face was hanging off. I could've been blown up with a lot of others. There are people standing aimlessly in the street."
Another eyewitness called Angie said: "There was a whole crowd of people around the bus and the next thing I knew I'm on the floor.
"Someone fell on me - I just ran into the nearest building. The bus was ripped off at the back - it couldn't have been anything else but terrorism."
An eyewitness in the Tavistock Place area told Sky News: "I was walking along. There was a whole crowd of people around the bus. The next thing I knew I was on the floor. There was shedloads of glass raining down.
"Someone fell on me and someone fell on him. For a moment I thought I was going to be trampled.
"I picked myself up and everyone was running. There was glass everywhere.We ran into a building and a security guard was saying `get in, get in'. Then the security guard said `get out' which was a bit scary.
Asked about the possibility of a terrorist attack, she said: "I saw the bus ripped out at the back ... it couldn't have been anything else."
Kurush Anklesaria told Sky Online: "I was on the train going from Bayswater station sitting in the first compartment of the train and after passing Paddington station at around 8.50am there was a huge blast just at the side of my feet and part of the floor was reeped open and flew up on the top of the tube.
"The whole compartment was full of smoke and I was covered in debris. I was brought down from the front of the train and walked on the rails to the Edgware Road station. I walked to my house and I am at home pretty shaken by the incident."
Another said: "The roof of the number 59 bus had been torn off during the blast near Russell Square in central London.
"Passengers from the nearby Russell Square Underground station were evacuated - some on stretchers."