Two people have been killed and scores have been injured after at least seven blasts on the Underground network and a double-decker bus in London. Latest reports say there are still people trapped in Kings Cross and eyewitnesses have reported that the bus was left ripped open without its roof.

UK Prime Minister Tony Blair said it was "reasonably clear" there had been a series of terrorist attacks.

He said it was "particularly barbaric" that the attack was timed to coincide with the G8 summit which he would be leaving to return to London, though he plans to return again this evening.

London's police chief Sir Ian Blair said traces of explosive had been found at one site.

He urged people to stay where they were and not to call emergency services unless it was a life-threatening situation.

Sir Ian said there had been "many casualties" but it was too early to put a figure to those killed or injured.

He reassured the public that an emergency plan was in place and the situation was "steadily coming under control". He advised people not involved in the blast to stay where they were.

A spokesman for Vodafone said emergency services were being given priority access to the mobile phone network which was causing problems for others, as many have reported difficulties getting through to families.

Hospitals have advised that they are accepting no further non-emergency cases and are said to be on major incident alert, as injuries and casualties are reported across the capital. Exact figures are not yet known.

"The health services are in support to deal with the terrible injuries that there have been," Clarke told reporters outside Downing Street.

A spokesperson for the City of London police said, "We believe there was some sort of explosion. There are some walking wounded at Aldgate. We are not sure of the scale of the incident. Reports are still coming in."