By Friday though, determined Londoners were back on mass transit making the morning commute to work.
"We are convinced that the politics we represent will win and triumph over terror," said Prime Minister Tony Blair, speaking from the G-8 economic summit in Scotland on Friday.
British Foreign Secretary Jack Straw said the attacks bore all the hallmarks of al Qaeda, though authorities are still investigating who is behind the blasts. A previously unknown group, "Secret Group of al Qaeda's Jihad in Europe," claimed responsibility on an Islamic Web site.
Police do not know, however, whether suicide bombers carried out the attacks or whether bombs had been left on the Underground or in buses.
Blair said Thursday afternoon that an intense hunt for the bombers is a high priority. "There will, of course, be the most intense police and security service action to make sure that we bring those responsible to justice," he said after meeting with the government's Emergency Committee, CNN reported.
Eric Draper / EPA / Landov
At the scenes of the explosions, bloodied and bandaged witnesses reported panicked crowds fleeing the sites.
"I was on the last carriage (of the Underground) when there was a loud explosion. The carriage filled up with smoke," Christine O'Connor, a 31-year-old teacher who narrowly escaped injury on London's subway system, told PEOPLE. "One of the (transportation staff members) escorted us through the tunnel. As we made our way back, I saw a man, possibly dead, on the tracks. There was no panic, but we were shocked."
A passenger on another underground train said that people were stunned, but calm after they heard an explosion nearby. "I didn't think too much of it (at first). You hear loud noises on the tube all the time," Leon Pye, 19, told PEOPLE. Pye said the relative calm was broken, however, after an emergency message asking people to evacuate the train was broadcast. "As soon as people heard it, it was like a concert, people pushing, shoving their way up the escalator."
TV coverage showed the entire top deck of a double-decker bus peeled back like an open sardine can as a result of one of the explosions. Police said the bus was located at Russell Square in central London.
Speaking at the G-8 conference, President Bush warned Americans back home to be "extra vigilant" as they headed to and from work. The terror alert in the U.S. was raised to code orange for mass transit systems only.
During the day, Prime Minister Blair returned to London, then went back to the G-8 meetings late in the day.
"Whatever they do, it is our determination that they will never succeed in destroying what we hold dear in this country and in other civilized nations throughout the world," Blair said, in reference to terrorists.
Americans concerned about loved ones in London may call 1-888-407-4747 for information.