A fire near a railway line is causing major travel disruption on the trains and the roads.
This incident, which began at Waltham Cross near the M25, has led to all train services through the area being halted, with rail routes towards Liverpool Street now being diverted via Seven Sisters.
Greater Anglia says the disruption is expected to continue until further notice.
A spokesperson for Greater Anglia said: "Unfortunately, we have received reports of multiple fires close to the railway lines and as a result, and a safety precaution, the London Fire Brigade have instructed that all train movements in the area be stopped."
Affected routes include Liverpool Street to Stansted Airport, Liverpool Street to Cambridge North, Stratford to Meridian Water, and Stratford to Hertford East.
Network Rail and emergency responders are currently at the scene working to extinguish the fires and restore train services.
Trains may be delayed, altered, or cancelled with little warning.
Services bound for London Liverpool Street are currently being diverted via Seven Sisters, while Hertford East to Stratford trains will instead terminate or begin at Liverpool Street.
Stratford to Meridian Water trains are cancelled.
In addition to rail disruption, drivers are being warned to take extra care on the M25 between junctions 25 (Enfield) and 26 (Waltham Abbey), where smoke from the fire is affecting visibility on the carriageway.
Alternative travel options are in place for affected passengers.
Greater Anglia tickets are being accepted on London Underground services, as well as on Great Northern, Thameslink, London Buses, and London Overground routes.
Passengers travelling between Stratford and Hertford East may use services via Liverpool Street or the Central Line on the Underground.
Stansted Express journeys are also being significantly affected, with estimated travel times of up to two hours and 30 minutes.
Passengers travelling from London Liverpool Street to the airport are advised to take Underground services to Kings Cross St Pancras, board a Great Northern train to Cambridge, and then transfer to a train to Stansted Airport.
For the return journey towards London Liverpool Street, passengers should travel from Stansted Airport to Cambridge, then take a Great Northern service to Kings Cross, followed by an Underground train to Liverpool Street.
Greater Anglia and Network Rail have apologised for the disruption.
The operator is allowing advance ticket holders to travel on earlier or later services if their booked train is cancelled.
Passengers delayed by 15 minutes or more may be entitled to claim compensation through Greater Anglia's Delay Repay scheme.
Further updates and travel advice are available on the Greater Anglia website.
