LONDON, England (CNN) -- Four explosions in London's transport system have killed at least two people and wounded dozens more in what UK Prime Minister Tony Blair said was an apparent terrorist attack.
More fatalities were sure to follow -- emergency services personnel told CNN that a rescue operation at Kings Cross station had successfully evacuated all survivors, leaving dead below ground "in the double digits."
Three of the blasts took place in the city's subway system and one more hit a double-decker bus, all at the height of rush hour.
International SOS, an international medical emergency service, reported that the police had found explosive traces in at least one of four confirmed blast locations.
Hospital officials have reported at least 160 wounded. London transit officials shut down the entire Underground and stopped buses in the central city district.
"We are dealing with large numbers of casualties," he said, "and we believe a number of fatalities."
Blair, in Scotland where he is hosting the G8 summit, told reporters he would leave the summit for a "face to face" report in London and then return later in the evening.
"It's reasonably clear there have been a series of terrorist attacks in London," Blair said. "There are obviously casualties, both people that have died and peole that are seriously injured.
Blair said it was "also reasonably clear" that the attacks were timed to coincide with the opening of the summit.
"It's particularly barbaric that this has happened on a day when people are meeting to try to help the problems of proverty in Africa and the long-term problems with the environment," he said. (Full text)
A White House spokesman said President Bush is aware of the explosions and had been in briefings with Blair all morning.
Despite calls from officials to stay home, however, Londoners were on the streets except in areas where they were barred by police.
Police cordoned off areas around six stations in and around the city's center and financial area and brought in sniffer dogs to check the areas.
Telephone traffic -- particularly by cell phone -- was nearly impossible. London's largest cellular provider, Vodaphone, said it had devoted much of its network to emergency services, causing the problems with subscribers.
London's police chief said the explosions, which began at about 8:50 a.m. (3:50 a.m. ET), certainly appeared coordinated.
One man, with blood streaming down the left side of his face from a wound on his temple, said he didn't "want to live through it again."
"I was in the front carriage and people were severely injured there," he said, dispassionately, adding that his train had been in the tunnel between Kings Cross and Russell Square. "I heard, but I don't know, that people were hurt worse further back. "Some people were very calm, others very panicky."
"There was a very loud bang, the lights went out, the carriage filled with smoke," he said. "We were all thrown forward."
Another man, clearly shaken by his experience, described being on a smoke-filled carriage on the same train, he and his fellow passengers afraid to try to leave the train.
"We were all trapped like sardines waiting to die," said Angelo Power. "I honestly thought I was going to die, as did everyone else."
A police spokesman urged Londoners to "stay where you are."
"There's no way to travel around London at the moment," he said.
"There is a London emergency plan," he said. "It has been put into effect. It is being coordinated by the Metropolitan Police, and that's about all I can say at the moment."
Scotland Yard sent out a notice saying that "public transport in London will be affected in the next few days."
Claire Burroughs, spokeswoman for St Mary's Hospital in central London, told CNN the hospital was on "major incident alert." Four patients were critically injured, eight were seriously injured and 14 others were being treated for minor injuries, she said.
"The types of injuries we are seeing include limb damage, burns, cuts, breaks, head injuries and chest problems due to smoke inhalation," Burroughs said.
London Hospital said it received 95 patients, most with minor injuries. Ten, however were listed in serious condition and seven in critical condition as well as "numerous with significant orthopedic injuries requiring immediate surgery."
CNN cameraman Oran O'Reilly said he has seen seven of the city's famed double-decker buses as well as police cars and ambulances arriving with casualties.
Another hospital told CNN it had taken in 40 wounded.
British Home Secretary Charles Clarke said the explosions took place between Russell Square and Kings Cross Underground; near the Moorgate, Aldgate and Liverpool Street stations Underground; and the Edgware Road station.
The fourth explosion on a bus just outside Tavistock Hotel.
London Metropolitan Police, British Transport Police and London's fire brigade are investigating, according to Scotland Yard.
O'Reilly, who was at Aldgate station, saw passengers coming out of it with signs of smoke inhalation -- black smudges around their mouths and noses.
"They're pushing people away from the tube (train) station," O'Reilly said. "Police are telling us to evacuate the street."
Also at Aldgate, CNN producer Roger Clark said he had seen people with blood running down their faces, with many others looking stunned.
An eyewitness who was on a train told Clark the car in front of him exploded and then the the train tunnel filed with smoke.
Separately, the London Fire Service said it was responding to a report of an explosion on a bus at Russell Square. Chamberlin heard a loud explosion in central London. Witnesses told him they saw a heavily damaged double-decker bus.
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