Rail services on the c2c line from Fenchurch Street to Rainham are being closed for two days after Christmas for engineering work ready for the new TfL extension to Barking Riverside.
No c2c-operated trains will run in either direction on Friday and Saturday, December 27 and 28, passengers are warned.
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This affects passengers from Limehouse, West Ham and Barking stations.
Passengers heading for Grays and Tilbury can switch to a bus replacement service from Upminster on those two days. Upminster station car park is also likely to be busier than usual during the Rainham branch closure, commuters are advised.
Before that, a special Christmas Eve timetable operates on the Fenchurch Street network with an earlier shutdown than usual, the last train to Shoeburyness leaving at 10.04pm. There are no c2c trains on Christmas Day and Boxing Day.
But things pick up with extra late-night trains on New Year's Eve to and from Fenchurch Street to get passengers home from celebrations. A reduced Sunday service runs on New Year's Day.