Commuters have been told not to travel from London Waterloo during the rush hour after a fire closed nine platforms.
The lineside blaze damaged cabling outside the station, meaning trains cannot use platforms 16-24.
Network Rail said “significant damage” had been caused to equipment, meaning trains will be delayed or cancelled.
Disruption is expected for the rest of the day while the Thursday morning rush hour may also be affected.
Network Rail said its engineers would be working through the night to fix the damage.
Waterloo is the busiest and largest railway station in the UK.
The platforms which are closed are normally used by trains serving Windsor, Reading, Hounslow, Richmond and Kingston.
However, services from other platforms are also being affected because trains have to be diverted or revised.
- Circular services via Hounslow, Richmond, Strawberry Hill and Kingston have been cancelled
- Trains between Waterloo and Windsor & Eton Riverside are diverted via Kingston
- Trains between Waterloo and Exeter/Salisbury are terminated and will restart from Basingstoke
Passengers were warned that services on other routes may also be subject to short-notice cancellations or delays.
In a joint statement, Network Rail and South Western Railway said commuters were “strongly advised to use alternative routes where possible and check their journeys before travelling at southwesternrailway.com for ticket acceptance and service details”.
Some passengers took to social media to express their frustration at the travel disruption.
One Twitter user described the situation as an “absolute shambles”, while others complained about being given the wrong or no information at all by train station staff.