But there was no panic; simply resolve not to let the attacks disrupt normal life.
"I am not worried. I get more angry, actually, rather than worried...about them trying to disrupt our lives, and trying to do this sort of thing. But it won't stop me from coming into London or stop me from going into work, or anything like that," said 28-year-old Irene, a Londoner who was sent home from her office near the Warren Street subway station, the scene of one of the incidents. "You know, you can't just stop living because of these people who are trying this sort of stuff. It's just not right. I think Londoners are made of pretty strong stuff, and they'll carry on coming to work, carry on coming to the city, as they have always done, basically."
Joanna, 33, works next to the Warren Street station.
"I think usually we're concerned on the day the trouble happens, and after that, we feel a bit more secure -- after a day or two," she said. "We're a bit used to it over here."
Reports say casualties from the latest attacks might have been limited by the possible failure of the devices to trigger a large blast. Investigators are looking at the remains of the devices to find fingerprints or other clues that could lead to the perpetrators.
London Metropolitan Police Commissioner Ian Blair said police believe the intention of the devices was to kill people in a manner similar to the 7 July London attacks, which left at least 56 people dead. But whether the latest attacks are connected to the earlier bombings remains to be determined.
"I don't think I am in a position to say that it is connected. I think that will take a little time. There is a resonance here, isn't there? I mean, these are four attacks; there were four attacks before," Blair said. "Whether or not this is directly connected in the sense that it was carried out by the same group of people, however loosely -- I think it's going to take just a little bit longer before we can qualify that."
Fifty-eight-year-old Charles works at University College Hospital, which is next to the Warren Street subway station. He and his co-workers were sent home after special police squads searched the grounds, apparently believing that one of the attackers may have been hiding on the premises.
"We're not worried at all. We're just -- we'll get on with our lives, and they won't deter us," he said. "We work in the hospital that they've just got the siege on at the moment, and everybody there has good spirits. It won't bother us at all."
Tony, 31, works as a computer specialist in a nearby block of offices. He said he's angry at Islamic extremists who are being held in detention in Britain.
"I am annoyed now because of all this going on now. I think they should -- and I think everybody feels the same -- send these people back to their country," he said. "These people who are in prison, you know, send them back. No more argument. Let's be gone with them, you know. I think we've all had enough now."
Sharon, a shop assistant, was amused by Londoners' resilience.
"The good thing today is that rumor has it there were no injuries or no deaths. But no violence is bearable, but don't you think that when something like this happens, nobody will defeat London, will they?" she said, and added in a reference to a group of Hare Krishna followers playing music nearby, "You know, you get the Hare Krishna. I think it's wonderful."
Twenty-five-year-old David is an accountant who is rushing to see some clients. He said he's optimistic that police may find the latest bombers because so much of the devices remain intact.
"There is not a lot you can do about it, so there is not a lot of point in worrying, really," he said. "If it happens, it happens, doesn't it? It is a bit more encouraging than last time, I suppose, isn't it?"
There has been no claim of responsibility for the attacks.
Prime Minister Tony Blair appealed for calm in the wake of the incidetns, urging Britons to continue with their business as normally as possible.