Explosions struck three London Underground stations and a bus at midday on Thursday in a chilling but less deadly replay of the suicide bombings that killed 56 people two weeks ago.
Only one person was reported wounded, but the lunch-hour explosions caused major shock and disruption in the capital and were hauntingly similar to the July 7 bombings by four attackers.
The London police commissioner confirmed Thursday that four explosions took place in what he described as "a very serious incident."
"We've had four explosions-- four attempts at explosions," Metropolitan Police Commissioner Ian Blair said outside police headquarters at Scotland Yard.
"At the moment the casualty numbers appear to be very low... the bombs appear to be smaller" than those detonated July 7.
Police also said an armed police unit had entered University College hospital. Press Association, the British news agency, said they arrived shortly after an injured person was carried in.
Sky News TV reported that police were searching for a man with a blue shirt with wires protruding. In a memo to hospital staff, officers asked employees to look for a black or Asian male, 6' 2" tall, wearing a blue top with a hole in the back and wires protruding.
The explosions did not shut down the subway system, although three lines remained closed more than two hours later. Blair appealed to Londoners to stay where they are until they hear more from police.
"What we don't want is lots of people going to railway stations," he said.
One witness told The Associated Press he smelled something similar to an electrical fire.
Police in chemical protection suits were seen preparing to enter the Warren Street Underground station. Sky News reported that police said no chemical agents were involved in the explosions.
Explosions also were reported at the Shepherd's Bush and Oval stations.
Emergency teams were sent to all three stations after the incidents, which began at 12:38 p.m. One witness told Sky TV that another subway passenger told him a backpack exploded at Warren Street and there were reports of smoke.
Stagecoach, the company that operates the stricken bus, said the driver heard a bang and went upstairs, where he found the windows blown out. The company said
Associated Press reporters Thin Lei Win and Kate Bouey in London contributed to this report.