A New Zealander working for Reuters in London says two colleagues witnessed the unconfirmed shooting by police of two apparent suicide bombers outside the HSBC tower at Canary Wharf in London.

The New Zealander, who did not want to be named, said the killing of the two men wearing bombs happened at 10.30am on Thursday (London time).

Following the shooting, the 8000 workers in the 44-storey tower were told to stay away from windows and remain in the building for at least six hours, the New Zealand man said.

He was not prepared to give the names of his two English colleagues, who he said witnessed the shooting from a building across the road from the tower.

Reports of attacks carried out by suicide bombers have been rife in London.

Canada's Globe and Mail newspaper reported an unconfirmed incident of police shooting a bomber outside the HSBC tower.

Canadian Brendan Spinks, who works on the 18th floor of the tower, said he saw a "massive rush of policemen" outside the building after London was rocked by the bombings.