Police and ambulance crews rushed to search rubble at the site in London's Bow district after the construction crane toppled across a building site and two adjacent houses on Wednesday afternoon.

London Ambulance Service tweeted that it had "treated four people at the scene" and taken two of them to hospital with head injuries.

"Sadly, despite the efforts of emergency services, a fifth person has been found and died at the scene," the service said in a later tweet.

Graham Ellis, assistant commissioner of the London Fire Brigade, said the crane had "collapsed onto a block of flats under development and into two terraced houses".

"Our Urban Search and Rescue crews are undertaking a complex rescue operation and using specialist equipment to search the properties," Ellis said, adding that the fire service had deployed a drone to help with the rescue operation.

Australian Associated Press