Disruption caused by a derailed freight train will continue for several more days, according to Network Rail.
Eleven carriages came off the tracks at Queen Adelaide near the Ely North junction, Cambridgeshire, on Monday.
The line is still blocked, affecting passenger services from Peterborough and Cambridge to Stansted Airport and London.
Network Rail would not be drawn on the nature of the freight involved, or the speed of the train at the time.
Rail accident investigators remain at the scene.
The 33-carriage freight train had been travelling from Felixstowe to Doncaster when the accident happened at about 14:30 BST on Monday. No one was injured.
A spokesperson for Network Rail confirmed there was "significant damage to the track" and that recovery by crane would take several days.
Simon Ancona, Network Rail's chief operating officer for Anglia, said: "The recovery is very complex and not helped by the rural location and will take several days.
"I understand how frustrating this is for passengers and would like to thank them for their patience while we work to get services up and running again."
The incident has severely affected Cross Country, East Midlands Trains and Abellio Greater Anglia passenger services.
Rail operator Greater Anglia apologised to passengers, adding that services would be cancelled, delayed or suspended until the line was cleared.
Similarities have been drawn between the derailment and another 10 years ago when carriages were left teetering over the river Ouse between Ely and Soham - on the same line.
The derailment, in June 2007, closed the line for six months. Network Rail had to create a 1.3km access route to the site to recover the stricken wagons.