Debris fell on to railway tracks in the accident on Wednesday night, leading to the closure of Liverpool Street station in London.

A National Express East Anglia train hit the debris but no-one was hurt.

Liverpool Street station remained closed during the morning rush-hour, which meant National Express East Anglia trains had to start and finish short of central London.

This affected passengers using Stansted Express services to Stansted airport in Essex as well as passengers travelling to and from parts of Essex, Cambridge, Norwich and Ipswich.

National Express East Anglia trains were starting and finishing at Stratford, Tottenham Hale or Hackney Downs, with passengers being forced to complete their commutes by Tube or bus.

Neighbouring train companies c2c and First Capital Connect were accepting National Express East Anglia passengers.

The affected bridge - GE19 - is just outside Liverpool Street station and was being worked on by engineering companies Balfour Beatty and Carillion on behalf of Transport for London (TfL).

Part of the new East London line which will open in 2010, the bridge had been constructed about a month ago and work was being carried out to move it into its final position.

A TfL spokesman said: "The contractors were jacking up the bridge. The jack collapsed and debris from the supports for the bridge fell on to the tracks. We are investigating the incident."