A tree has fallen onto railway tracks, causing major delays and cancellations for train passengers.
The incident is affecting services through Stansted Mountfitchet, with disruption expected until 8.15pm on October 23.
Stansted Express has advised customers not to travel between Broxbourne and Stansted Airport until further notice.
A spokesman for Stansted Express said: "We have been informed of a tree blocking the railway in the Stansted Mountfitchet area, which is also affecting the power in the overhead electric wires.
"Network Rail response teams will be on site to investigate by 6.30pm."
Routes affected include Stansted Express services between London Liverpool Street and Stansted Airport, as well as services between Liverpool Street and Cambridge North, Broxbourne, Stratford and Bishop’s Stortford, and Stratford and Meridian Water.
Passengers who cannot postpone their journey can use their tickets on alternative routes at no extra cost.
These include the Circle, Hammersmith & City, and Metropolitan lines between Liverpool Street and Kings Cross St Pancras, the Victoria line between Tottenham Hale, Finsbury Park, and Kings Cross St Pancras, and Great Northern services between London Kings Cross and Cambridge.
Stansted Express has issued alternative travel advice for those heading to the airport.
Passengers are advised to travel from London Liverpool Street to Kings Cross St Pancras using the Circle, Hammersmith & City, or Metropolitan lines, then take a Great Northern service to Cambridge, and change at Cambridge for a train to Stansted Airport.
The total journey time is expected to be up to two hours and 30 minutes.
For those travelling towards London Liverpool Street, the advice is to take the first available train from Stansted Airport to Cambridge, then change for a Great Northern service to Kings Cross, before using the Circle, Hammersmith & City, or Metropolitan lines to reach Liverpool Street.
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