The woman, named locally as Emily Diamond from Abbey Wood, south east London, died at the scene of the accident on Tower Bridge Road.

The accident happened at the junction of Tower Bridge Road and Tanner Street as the route 188 bus travelled between Russell Square and North Greenwich station.

The 23-year-old, believed to be a pedestrian, was pronounced dead at the scene. Nine people were taken to hospital following the incident, police said.

Witnesses said the accident was caused when a large tree branch smashed into the double-decker.

The branch is believed to have hit the right-hand corner of the bus, denting the roof and shattering glass in the front windows, both in the top and bottom deck.

Builder Tom Riley, 32, of Tottenham, north London, said: "I was coming out of the van and heard a crack. The bus driver stopped and we tried to get on the bus and kick the door in. Then the bus driver collapsed.

"There was about 20 people in total on the bus and quite a few were old people. At first we thought it was a bomb. It was as if the tree was just falling and was slowing the bus down."

He added: "We did not realise that there was somebody under the tree. We just thought that it was the people in the bus who needed help."

Tower Bridge was closed and bus routes 1, 42 and 188 were diverted following the accident. The next of kin of the fatality are still in the process of being informed.