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The remnants of the bus that exploded near Tavistock Square, central London, Thursday, July 7. (AP photo).

Britons are awakening to discover that Thursday's co-ordinated series of attacks in London killed at least 52 people, making it the deadliest attack on London in more than 30 years.

The bombings, which came without warning, also injured more than 700. Police and hospital officials say that the severity of some of those injuries means the number of dead will increase in the days ahead.

Late in the day police would only confirm 38 deaths. But newspapers in the British capital say emergency officials underestimated the number killed on a London double-decker bus. Initial reports said two people died when the bus exploded. But it now appears at least a further 15 people riding on the bus were killed.

Thirty-five others died when three separate bombs exploded in the London Underground during Thursday morning's rush hour.

Scores of people suffered serious or critical injuries such as burns, severed limbs, chest and head injuries in Thursday's attacks.

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Pedestrians pass St. Paul's Cathedral, London, Thursday, July 7. (Jack Guez / AFP / Getty Images))

Hospitals set up emergency treatment areas for the injured people, many whom were covered in soot and blood.

British Prime Minister Tony Blair said it's "reasonably clear" the "barbaric" attacks were the work of terrorists and were aimed to coincide with the opening of the Group of Eight summit in Scotland.

"The purpose of terrorism is just that. It is to terrorize people. And we will not be terrorized," Blair said.

"They are trying to use the slaughter of innocent people to cow us," he said. "They should know they will not succeed," he said.

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Injured tube passenger is escorted away from London subway station. (AP Photo)

British Home Secretary Charles Clarke has confirmed four blasts took place:

  • Between Aldgate East and Liverpool Street subway stations. (7 dead)
  • Between Russell Square and King's Cross subway stations. (21 dead)
  • At Edgware Road subway station. (7 dead)
  • On a bus at Woburn Place near Tavistock Square. (2 confirmed dead - 17 dead according to media reports)

First reports from subway stations

The first reports of subway blasts came at 8:51 a.m. local time, sending fire trucks and ambulances to the scenes.

About an hour later, at 9:47 a.m., the roof of a double-decker bus was blown off and its sides peeled back near Tavistock Square in central London.

Loyita Worley was on a subway train going between Liverpool Street and Aldgate stations when an explosion rocked the next car.

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Paramedics on the scene at Edgware Road Tube Station in London following an explosion, Thursday, July 7. (AP photo)

"We heard banging from the next carriage, people shouting for help," she told CBC Newsworld.

"They called for medical assistance and various people went up – nurses, doctors and so on."

Later, she said, "they brought all the walking wounded through," including people blackened by smoke and commuters with some or all of their clothes torn off by the force of the blast.

Making her way out of the train and along the tracks to the nearest station, she said she saw at least one body and many injured people.

Worley said she is still stunned by what happened, though she was used to anti-terrorism drills from 30 years of working in a city under the constant threat of Irish Republican Army attacks.

"I was just so pleased it wasn't me," she said. "I was just thanking my lucky stars, thanking God that I was OK."

A man on a subway car said the situation was terrifying.

"There were flashes of light, people were screaming and smoke began to billow into the carriage," said lawyer Angelo Power. "We were trapped like sardines waiting to die."

No information on bombs

Officials initially blamed a power surge for the subway blasts, but that changed after police found evidence of explosive material at two explosion sites.

Police say it's too early to tell whether the explosions were caused by suicide bombers or bombs left in the stations and bus. They also couldn't provide any information on what type of explosives were used, but said that they were "deliberately designed to kill and injure innocent members of the public."

There have been no confirmed claims of responsibility, but police said they are investigating a claim from a group calling itself "The Secret Organization of al-Qaeda in Europe." The web site said the attacks were carried out in retaliation for Britain's involvement in Iraq and Afghanistan.

"We don't know if it's a genuine claim or not," said a police spokesperson.

Foreign Affairs has set up a hotline for Canadians with strong reasons to believe their Canadian relatives might have been travelling on London transit. They should have on hand the missing person's full name, date of birth and passport number before calling the toll-free hotline at 1-800-606-5499.

As many as three million people use the London Underground each day. It's the world's oldest subway system and one of the largest in the world.