Wounded Londoners painted a nightmarish picture of chaos and bloodshed as a string of explosions ripped through the heart of the city yesterday.

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

Christine O'Connor was on a Circle Line train at Edgware Road Station, west of the centre.

"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," she said.

One explosion ripped a red double-decker bus open like a tin of sardines near Russell Square - a popular area for tourists.

Casualties staggered from the scene.

"I was on the bus. I looked round and the seats behind me were gone," a middle-aged victim said, too shocked and disoriented to say more.

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

Loyita Worley, 49, was travelling from Moorgate to Aldgate station in the City financial district when her underground 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, which had been torn from "floor to ceiling".

"Many were shaking, there were a lot of head injuries, it was very bloody," she said.

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.

Andrew Allwright, 42, a business development manager at Reuters, narrowly escaped injury at Aldgate East station.

"As I was walking up the steps there was a loud bang behind me and I felt a blast of air coming from behind. I turned around and saw dust rising from the station," he said. 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 centre were cancelled. They stood empty and silent, warning lights flashing.

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

A terrifying picture began to emerge of the carnage that followed the bus blast on Woburn Place near Russell Square.

"It was a huge, huge explosion - chunks of building were flying in the air," said Doug Streeter, who was about 150 metres away from the blast at about 0810 GMT.

"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," he said. "At the time I couldn't see it was a bus exploding."

Peter Gordon was working in an office overlooking the scene. "The roof of the bus was blown off, there was smoke everywhere," he said. "It was carnage, you could see bodies on the roadside alongside."

A quiet panic spread around the scene, which police rapidly sealed off.

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

Angelo Power, a barrister emerging from the station, said a loud explosion rocked his train as it left King's Cross. There were flashes of light, people were screaming and smoke began to billow into the carriage.

There was mayhem as 20 to 30 minutes passed before police reached the train to take survivors to safety. Women passed out and agitation turned to hysteria as people smashed the glass windows to escape billowing smoke but feared jumping out on to what they thought could be live electric lines.

"We were trapped like sardines waiting to die, he said. Asked what he thought of the people who may have been behind the attacks, he said: "I pity them."