Rail services connecting parts of Norfolk, Suffolk and Essex with London are severely disrupted due to damaged overhead electric wires.
All lines are blocked between Ipswich and Manningtree because of the problem, Greater Anglia said.
The damage was reported on Thursday afternoon but is so extensive it is expected to cause disruption for the rest of Friday.
The wires were wrapped around a train, which was removed from the scene shortly after midnight.
A limited replacement bus service is being provided between Colchester and Ipswich.
The disruption comes amid a surge in demand for travel to London as mourners pay their respects to the late Queen.
Greater Anglia is among the operators running extra services to ease journeys.
The company said in a statement: “Network Rail engineers are working to complete the necessary repairs as quickly as possible, but the extent and nature of the damage mean that it is currently expected to take until the end of Friday before the work is finished and a normal service can be restored.
“We’re very sorry for the inconvenience this disruption will cause to passengers’ journeys.”
Ellie Burrows, Network Rail’s route director for Anglia, said: “I am really sorry to passengers who are affected by the ongoing issues in Suffolk.
“Our engineers have been working since the incident to remove the train and repair the overhead wires.
“The damage is extensive and it will take us until the end of the day to fix.
“A rail replacement service is in operation.
“Once again I apologise for the disruption and advise anyone travelling through the affected stations to check with the train operator before they travel and allow extra time to complete their journeys.”
