People travelling from Suffolk to London for the New Year will have to make part of their trip by bus because the line will be closed near Chelmsford.
Engineers are building a new station at Beaulieu Park north of Chelmsford and the line will be closed from Christmas Eve and reopen on January 2.
Buses will replace trains between Witham and Billericay between December 27 and January 1 and passengers should allow an extra hour for their journeys during this time.
The whole rail network in East Anglia will close down on the evening of Christmas Eve and will not restart until December 27 - the only trains running will be a few Boxing Day services between London and Stansted Airport.
On other lines there will a few changes over the Christmas period and people are being urged to check timetables before they travel, but most trains will run as normal.
People from the west of Suffolk heading to London via Cambridge will also face disruption because Network Rail is also building a new station south of that city which will also mean that Ipswich to Cambridge trains will stop at Bury St Edmunds with a bus link west.
Katie Frost, Network Rail's route director for Anglia, said: “Our programme of engineering work this Christmas is critical for upgrading and maintaining the railway ahead of the new year.
"Our engineers, maintenance crews, contractors and surveyors will be out on track over the entire Christmas period delivering this important work.
“We have a significant Christmas programme this year, particularly around Cambridge and Chelmsford to continue building new stations planned to open in 2025.
"I’d like to reassure passengers that we’ll be getting a huge amount done while trains aren’t running and I want to say thank you to our lineside neighbours for bearing with us while we’re out working hard in their communities."
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