Injured Londoners and visitors to the British capital painted a nightmarish picture of chaos and bloodshed as a string of explosions ripped through the heart of the city Thursday.

Across the paralyzed capital, the wounded stumbled from tube stations devastated by blasts, telling of mayhem on the underground railway system.

Traffic wardens, police support officers and private security guards were drafted in to man cordons near the blasts around the city. All buses in the center were canceled. They stood empty and silent, warning lights flashing.

London's cell phone networks quickly became jammed with callers trying to reassure or reach loved ones, and shops filled with people begging to use the phone.

Ambulances sped from the wreckage of a bus torn apart by a blast near central London's Russell Square. Its mangled upper deck was open to the sky and debris littered the street. The facade of a nearby building was blackened and scarred by shrapnel.

Most of the explosions hit the underground rail network, which was immediately suspended, leaving many commuters trapped in tunnels as they awaited evacuation in the semi-darkness.

Christine O'Connor was on a Circle Line train at Edgware Road station, west of the center. ``I was in the last carriage, we pulled out of the station and then almost immediately there was an explosion, it just went very quiet. The carriage filled up with smoke.''

Loyita Worley, 49, was traveling from Moorgate to Aldgate station in the City financial district when her train was shaken by a large explosion.

``I saw an orange flickering on the side of the tunnel,'' she said, adding 20 to 30 walking wounded had been led from the damaged carriage. ``Many were shaking, there were a lot of head injuries, it was very bloody.''

One man's clothes had been blown off and he was totally black with soot, she said, but passengers remained calm even as debris fell down onto the roof of the carriage.

Emergency workers set up a medical command post in a Hilton hotel near Edgware Road subway station, where an explosion ripped through a crowded train.

A Swedish woman riding the underground toward the station said she heard the blast behind her train.

``Everything went black, and people threw themselves to the floor in panic,'' Cornelia Berg told Swedish newspaper Aftonbladet by phone. ``The car quickly filled with smoke and a lot of people used their umbrellas to try to break the windows so that we could get air. A mother with her two small children sat next to me and cried desperately.''

When passengers were evacuated, she said, there were body parts scattered around them.

American Sean Barron, 20, said he helped treat the wounded at Edgware Road station. ``One gentleman told me that the floor of the train he was on was blown out, it was just gone. I believe another gentleman was ejected from the train.''

Arash Kazerouni, 22, was traveling on the Underground from Liverpool Street. ``There was a loud bang and the train ground to a halt. People started panicking, screaming and crying as smoke came into the carriage. A man told everyone to be calm and we were led to safety along the track.''

The attacks also paralyzed all of London's bus routes after the explosion on the double-decker bus near Russell Square.

``The explosion seemed to be at the back of the bus,'' said Raj Mattoo, 35. ``The roof flew off and went up about 10 meters. It then floated back down.

``I shouted at the passengers to get off the bus. They went into Tavistock Park nearby. There were obviously people badly injured. A parking attendant said he thought a piece of human flesh had landed on his arm.''

Doug Streeter was about 150 meters from the bus blast. ``It was a huge, huge explosion,'' he said. ``My immediate thought was Olympics, G8, this is big, I don't want to be around here. Hordes of people were running for their lives.''

At least 20 ambulances queued to take away casualties from the bus explosion, while victims from a blast underground, apparently on a train from nearby King's Cross, were stretchered up from Russell Square station.

Biage Arnold, a transport worker at nearby Euston Station, said: ``They've been talking about this kind of thing in London, but you never think it's really going to happen.''

And her colleague, Arvind Mavji, said: ``Yesterday we were quite glad that we got the Olympic bid. Today we are wondering if it was worth it.''AGENCIES