At least two people have been killed as a series of six explosions have rocked London’s underground rail system during Thursday morning’s rush hour. It now seems that the incidents appear to be co-ordinated attacks to coincide with the start of the G8 Summit in Gleneagles, Scotland.

Buses were also reported to have been hit as eye-witnesses have stated that they saw the top ripped off a double-decker bus near Russell Square station close to King’s Cross terminal. They also saw the twisted wreckage of a second bus nearby.

A doctor at Aldgate underground station near the financial centre of the city said there were at least 90 casualties there.

The cause of the blasts, which occurred one day after London was awarded the 2012 Olympics, remains unconfirmed, but it is clear that many of London's underground stations were affected.

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

Another police spokesman stated, "There have been some casualties and this has been declared a major incident."

Security experts have commented that the way the explosions have occurred are alike to those previously used by terror network al Qaeda.

"If we what are looking at is a simultaneous bombing -- and it does look like that -- it would very certainly fit the classic al Qaeda methodology," said Dr. Shane Brighton, intelligence expert at the Royal United Services Institute for Defence.

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.

He added that, Number 10 was ‘still unsure’ whether the explosions were the result of a terrorist attack and that ministers are meeting to clarify the situation.