British Prime Minister Tony Blair blamed Islamic extremists and said the bombings were designed to coincide with the opening in Scotland of a G-8 summit of the world’s most powerful leaders. Foreign Secretary Jack Straw said the bombings — which came the day after London won the bid to host the 2012 Olympics — have the “hallmarks of an al-Qaida-related attack.”

A wounded person is taken to an ambulance at Kings Cross station, where several explosions tore through the London subway during the morning rush. Knight-Ridder photo

“I didn’t hear anything, just a flash of light, people screaming, no thoughts of what it was. I just had to get out of the train,” said subway passenger Chris Randall, 28, who was hospitalized with cuts and burns to the face, the legs and hands.

“It was chaos,” said Gary Lewis, 32, evacuated from a subway train at King’s Cross station. “The one haunting image was someone whose face was totally black (with soot) and pouring with blood.”

Police said there had been no warning and that the blasts at three subway stations went off within 27 minutes, starting at 8:51 a.m. local time in an Underground train just outside the financial district. Authorities initially blamed a power surge but realized it was a terror attack after the bus bombing near the British Museum at 9:47 a.m. — less than an hour after the first explosion.

It was the attack that Britain had long feared, following the Sept. 11, 2001, strikes in New York and Britain’s subsequent alliance with U.S. forces in Afghanistan and Iraq. Today’s explosions also recalled the March 11, 2004, terrorist bombs that killed 191 people on four commuter trains in Madrid, Spain.

There was no credible claim of responsibility, and police were investigating whether suicide bombers were involved. Al-Qaida did not issue claims of responsibility after the Sept. 11 attacks on Washington and New York.

The worst attack on London since World War II brought out a stoicism that recalled Britain under the blitz of German bombers.

As yesterday’s jubilation at winning the 2012 Olympics gave way to the terrible shock of today’s attacks, Blair rushed back to the capital and made a televised appeal for unity, praising the “stoicism and resolve of the British people.”

Both were in evidence across the city, as volunteers helped the walking wounded from blast sites, commuters lent their phones so strangers could call home and thousands faced long lines for homeward-bound buses or even longer walks without complaint.

“As Brits, we’ll carry on — it doesn’t scare us at all,” said tour guide Michael Cahill, 37. “Look, loads of people are walking down the streets. It’s Great Britain — not called ’Great’ for nothing.”

Security was raised in the United States and around the world. The Bush administration upped the terror alert a notch to code orange for the nation’s mass transit systems, and bomb-sniffing dogs and armed police patrolled subways and buses in the capital.

Much of Europe also went on alert. Italy’s airports raised alert levels to a maximum. The Czech Republic, Hungary, Russia, the Netherlands, France and Spain also announced beefed-up security at shopping centers, airports, railways and subways.

The bombings came as Blair and President Bush met over breakfast in Gleneagles, Scotland, and answered questions from reporters, and before all the leaders were due to begin the summit’s general session.

G-8 leaders stood in solidarity with Blair before the prime minister made his hasty departure for London to confer with his Cabinet.

“The war on terror goes on,” Bush said. “I was most impressed by the resolve of all the leaders in the room. Their resolve is as strong as my resolve.”

In London, police said they could confirm at least 37 people had been killed, including two in the bus attack. Three U.S. law enforcement officials told The Associated Press at least 40 were killed.

French Interior Minister Nicolas Sarkozy later said the death toll had risen to 50, citing a conversation with his British counterpart. This could not immediately be confirmed.

A spokesman for the U.S. Embassy in London said there were no initial reports of American casualties.

Police said at least 700 were wounded, many of whom emerged bleeding and dazed from the Underground. Among them, at least 45 were in serious or critical condition, including amputations, fractures and burns, hospital officials told The Associated Press.

The first blast caught a subway train between Moorgate and Liverpool Street stations, on the eastern fringe of London’s financial district. Seven died, police said. Moorgate is named for one of the gates in the city walls of London, of which few traces remain. Some people caught in the blast emerged from the Aldgate Station, near Jack the Ripper’s old haunts in Whitechapel.

The second bombing came five minutes later, on a second train deep underground between the King’s Cross and Russell Square stations. Police said 21 died. King’s Cross station, in one of the seediest parts of London, is the film setting for Platform 9 3/4 in the Harry Potter films. Russell Square station serves Bloomsbury, the early 20th-century literary hotbed where Virginia Woolf and luminaries lived. The British Museum is a short walk away.

At 9:17 a.m., there was an explosion involving two or perhaps three trains around Edgware Road station. Five people were killed, police said. Edgware Road is the heart of a thriving Arab community, and convenient to Hyde Park, scene of last weekend’s Live 8 concert.

The bus explosion took place near Russell Square, an area of many modestly priced hotels popular with tourists and close to the British Museum. Also nearby is the home where Charles Dickens lived from 1837 to 1839.

The explosions shut down a subway and bus system which handles 8.4 million passenger journeys per day, though buses started running again for the evening rush hour.

Stocks sank in Europe and on Wall Street, and the British pound fell to a 19-month low against the U.S. dollar. London’s FTSE 100 index fell about 2 percent, or 102.40 points, gaining back half its earlier losses. Germany’s DAX fell 1.8 percent and the CAC 40 in Paris was down 1.7 percent.

Theaters in London’s West End all canceled today’s performances.

Doctors streamed out of the British Medical Association’s offices when the bus blew up outside.

“There was someone in bits in the road,” said Dr. Laurence Buckman. “The front of BMA house was completely splattered with blood and not much of the bus was left.”

The driver was among the survivors, said bus operator Stagecoach.

Bystander Raj Mattoo, 35, said the roof of the bus “flew off and went up about 10 meters (about 30 feet). It then floated back down.”

Terrorism experts agreed with Straw that the explosions had the hallmarks of al-Qaida.

“This is clearly an al-Qaida style attack. It was well coordinated, it was timed for a political event and it was a multiple attack on a transportation system at rush hour,” said Lawrence Freedman, professor of war studies at King’s College in London.

Blair implicated Islamic extremists but cautioned that they speak for only a small percentage of Muslims.

“We know that these people act in the name of Islam, but we also know that the vast and overwhelming majority of Muslims here and abroad are decent and law-abiding people who abhor this act of terrorism every bit as much as we do,” Blair said.