Thousands of train passengers travelling from Bedfordshire, Hertfordshire and Northamptonshire are potentially facing severe delays until the end of the week due to "extensive" damage to overhead power cables.
The problems at Radlett in Hertfordshire led to major changes to services run by three train companies - Southeastern, East Midlands Trains and First Capital Connect (FCC) on Wednesday.
While East Midlands Trains were hoping to return to a full service on Thursday, provided Network Rail carries out necessary repairs tonight, delays on FCC trains could run into Friday.
The two companies both operate lines between London and Luton.
A half hourly train shuttle service will run between Bedford and Luton Airport Parkway (this will reduce to hourly from midnight)
Buses are running between Luton Airport Parkway and West Hampstead Thameslink, between St Neots and Bedford and also between Hitchin and Luton Airport Parkway
From midnight, buses will run between Luton Airport Parkway and London St Pancras
Trains are unable to run between Luton and London St Pancras International
Buses are running between Wellingborough and Northampton to connect with London Midland services between Northampton and London Euston
Buses will replace trains between Corby and Kettering
Unused tickets dated for today Wednesday 13 February are valid for travel tomorrow Thursday 14 February
"The delays are going to be running all day tomorrow," the First Capital Connect spokesman said.
"The damage is extensive - 1km of overhead power cables are down."
There will be trains serving every station on the FCC line on Thursday but there will be heavy delays of between an hour and 90 minutes, he said.
The final set of repairs is expected to be carried out from 10pm on Thursday night and customers are being advised to use buses or alternative train routes after this time.
But there may still be delays on Friday as trains will be displaced over the line, the spokesman said.
A spokeswoman for East Midlands Trains explained that their trains run on diesel and are therefore less reliant on the power cables than FCC trains.
She said: "Provided that Network Rail carry out the work that they are needing to do tonight we are planning to run a full timetable tomorrow morning."
She also urged passengers to check timetables before travelling on Thursday.
Passengers told the Watford Observer that they were evacuated from trains after the overhead power cables in Radlett collapsed.
After hearing a loud bang they had to wait for two hours on a train before being evacuated, walking down the railway line, according to the newspaper.
Bob Crow, general secretary of the RMT transport union, said: "RMT has been raising serious concerns about the shortage of overhead line crew and capacity on Britain's railways for a number of years now.
"The chaos on services hitting hundreds of thousands due to the massive breakdown through central London as a result of the lines down in Hertfordshire reinforces RMT's demand for a full review of OHL maintenance and emergency staffing numbers."