A series of explosions hit London's transport system during rush hour Thursday morning, causing a number of casualties and the suspension of the entire underground network.

Home Secretary Charles Clarke was cited by local media as saying that the blasts caused "terrible injuries," and police said there were at least 90 casualties.

There were no definite reports on the cause of the blasts, but police had defined them as "major incidents."

"It is too early to state what has happened," a London police spokesman said. "I cannot comment on reports of bombs, but we have had multi-reports of explosions around London."

The first explosion occurred near the area near Liverpool Street railway station and several people were reported injured. The subway maintenance company said a power surge caused the explosion.

London Underground reported a second incident at another subway station in northwest London, but gave no details.

Police evacuated several tube stations after the incidents, including the busy King's Cross station in north London, and shut down the whole railway network.

Not long after the underground blasts, three explosions ripped through buses in central London, causing casualties.

The first destroyed a double-decker bus at Tavistock Square in downtown London and there were no specific information on the rest two.

The explosions occurred one day after London was awarded the 2012 Olympics and as leaders of the G8 nations are meeting in Scotland for a summit.

Related News:

Photos: At least two dead, 90 injured in explosions in London

G8 leaders open annual summit amid London blasts

Blair condemns "barbaric" terrorist attacks in London

IOC: London bombing is not Olympics-related

At least two killed, 90 injured in London explosions

Source: Xinhua