The twisted, smoking wreckage of a red double-decker bus. The sidewalks slick with blood and body parts. Dozens of wounded people screaming in agony or stunned into silence.

This was the scene of devastation that confronted physician Laurence Buckman when he pulled up in front of his office in the British Medical Association building.

Within minutes, Buckman recalled, he and a dozen colleagues set up a makeshift MASH unit in the building's stately courtyard and started treating the victims. They worked for four hours, helping people with multiple fractures, burns, chest and head injuries and, in some cases, missing limbs. Two people died in the courtyard while doctors worked desperately to help them.

"We did what we could," a weary Buckman recalled in a telephone interview Thursday evening. "Did we save lives? I hope a few people had their chances of survival enhanced."

Throughout London, victims, witnesses and rescuers recalled a day that many had expected, even dreaded, but for which no one was quite ready. Some saw the dead; others expected to die themselves. The survivors emerged marked by bloodstains, soot and tiny shards of glass, and haunted by what they had seen and heard in the dark, suffocating tunnels where they waited to be rescued, or aboard a morning bus that suddenly exploded.

Fiona Trueman, 26, of St. Albans was aboard the Piccadilly Line train on which the most people were killed. "There was a massive bang, the train lights went out and there was a lot of smoke and glass smashing," she recalled. "There was four or five seconds, and then everyone was going, 'Oh my God, we can't breathe.' What was running round in my mind was: Am I dreaming? It was surreal. The bomb was in front of the train or on the tracks. I was in the second carriage. There was screaming and coughing with the smoke.

"It was pitch black and people were getting their mobiles," she said. "Everyone was screaming to break the windows. No one was telling us anything; there was no contact from the driver. I don't even know if he made it, to be honest. The screams from the carriage in front of us were terrible."

"I think the driver passed away," said 25-year-old Joseph Aka, another Piccadilly Line passenger. "Because when the train exploded, he didn't say anything after that.

"People started shouting, 'Help, help!' " Aka said. "No one came to help."

Survivors from the Piccadilly Line estimated they spent half an hour trapped in the blackness, smoke and blood of the subway cars. Some said they wept. Others strained to make conversation, asking strangers what work they did. The cries of the wounded made it difficult. "The screams from the carriage in front of us were terrible," Trueman said.

Passengers finally made it out through the mostly intact rear car. Feeling their way, they walked 15 minutes back to the King's Cross station, fearful all the time of electrocution from the tracks, Aka said. The strong helped the injured, walking past mutilated, motionless bodies, he said.

"People were still in their seats and they were screaming with pain," said Michael Henning, 39, a city employee who was aboard another subway line, the first believed hit. "There were other people that were trapped, and they were just left down there."

The blast hit the car Henning was riding in, he recalled, blowing out part of a metal wall and throwing seats from the train.

Passengers described the efforts of the train drivers and of the police, who struggled to pry open broken exits and lead people to safety.

Mindful of the wounded still left in the dark, Henning said, he pleaded with police to do more.

"When I got to the surface, I asked a fireman and a policeman that were just standing there why they were not going down to save people," he said. "I know they had a legitimate concern about a second bomb, but I said to them, 'There's sons and daughters down there. There's people dying.' "

Henning spoke at the Royal London Hospital, where scores of the wounded were treated after being ferried there aboard a double-decker bus doing duty as an ambulance. Henning walked out of the hospital with a large bandage covering one eye and a bloodied shirt and suit. A sticker on his chest bore the number 26, given him by police investigators who had taken his statement.

"We were left on the train for about 25 minutes," he recalled. "It was very dark all around us. People panicked and were screaming, and a few of us were telling them to calm down. The girls were the calmest, and they got things under control quickly. We tried to open the side doors, we were trying to pull them. The London Underground drivers were trying to get them open from the outside, but they weren't moving. There was a lot of dust and smoke. There was no communication, no feedback.

"We started moving down through the carriages to get off at the back of the train," Henning said. "I got to go forward because I had been injured. In my immediate carriage there was people with their faces covered in blood, and many were cut up.

"In the carriage that was hit by the bomb, there was part of the side wall missing," Henning continued. "Some of the seats were missing. People were still in their seats, and they were screaming with pain and were covered in blood down one side of their body. There were other people that were trapped and they were just left there."

Kabin Chibber, 24, who works in the Dow Jones building above Aldgate station, said the whole structure shook with the impact. "People were coming out covered in black soot, blood and a mixture of grease," she said. "There were people lying at the side of the station on plastic sheeting."

Derek Price, 55, of Essex was in the next car on the Circle Line train leaving Aldgate. "It was a huge explosion," he recalled. "A flash of flame went down the side of the train.

"There was lots of dense smoke very quickly, lots of grit and rubbish. It was very, very quick and everyone was on the floor," Price said. "After Aldgate it took me about 45 minutes to evacuate, we had to walk down the line. Some people were upset, but there wasn't panic considering you could only see a few feet in front of your face. It was a huge impact."

Caroline Chrobok, 31, an office manager from Finchley, in London, was covered with tiny cuts and bruises. "We were just trying to protect ourselves from the glass flying around, but we just ended up getting more cuts," she said. "I have perforated eardrums because of the blast. I thought that I was burnt because my face was really sore, but it's just scratches. They gave me some antibiotics and let me go."

Back at the British Medical Association building, Buckman, who is a family physician in north London, said doctors began with a quick triage, dispatching the lightly injured to a hotel lobby next door while dealing with about 18 more critical patients. "In 20 minutes you had what amounted to a field hospital," he said. "The whole thing became professionalized very quickly. We had an expert in emergency medicine who was on it instantly."

Some of the worst injured were the walking wounded, according to Buckman -- people who said they were fine but turned out to be in deep shock from the force of the blast. Everyone pitched in, he said. When doctors ran short of critically needed fluid bags, a policeman ran off to a nearby hospital and returned with dozens.

"You don't think of it as horrendous," Buckman said. "You just concentrate on the patient you're with."

Later, he said, he looked at the twisted wreckage of the bus again. "There's little of it left," he said. The medical association's headquarters, designed nearly a century ago by the architect Edwin Lutyens, was unscathed but for one detail. "The front of the building is spattered in blood," Buckman said.

Special correspondent Audrey Gillan contributed to this report.

A photograph taken by a passerby shows victims being helped near Tavistock Square in London after a bomb blast on a bus.A double-decker bus was ripped open after a bomb exploded on it during London's morning rush hour. Bombs also struck three trains. Prime Minister Tony Blair called the attacks "barbaric."Injured passengers are escorted away from London's Edgware Road station after a bomb exploded on a train pulling into the station, causing it to collide with two other trains. A survivor from the Piccadilly Line train on which the most people were killed said, "I think the driver passed away. Because when the train exploded, he didn't say anything after that."