A National Rail statement said all lines between London Kings Cross / Moorgate and Stevenage, Hertfordshire were closed following “a number of incidents”.
“Trains may be cancelled, delayed by up to 90 minutes or revised,” the statement said.
“Major disruption is expected until 09:00.”
Customers have been warned not to travel on routes which usually run through Stevenage after damage to overhead electric wires resulted in the closure of all rail lines via the station.
Services running through Tulse Hill in south London were also separately affected, due to an emergency services incident.
Flooding was also reported across London, affecting roads.
We're receiving numerous calls about flooding across London this evening with roads and properties affected.
Crews are working as quickly and as safely as they can to respond to calls.
If you've been affected by flooding, take a look at our advice: https://t.co/gbZEJ8S27n https://t.co/Mfdak6xtuR
— London Fire Brigade (@LondonFire) September 20, 2023
The London Fire Brigade said late Wednesday night: “We’re receiving numerous calls about flooding across London this evening with roads and properties affected.
“Crews are working as quickly and as safely as they can to respond to calls.
“If you're out on the roads, please do not drive through floodwater. A foot of moving water at just 6mph is enough to float a car. Always try and find an alternative route.”
The capital was under a yellow weather warning for rain until 3am, which warned of potentially longer journeys with bus and train services being affected and “spray and flooding on roads probably making journey times longer”.
Sunny intervals are expected in London in the morning, before changing to cloudy by late morning and rain in the afternoon, before easing in the evening.
Met Office meteorologist Aidan McGivern said: “A band of rain will clear by the start of Thursday and that will be followed by sunny spells and showers with low pressure never too far away from the UK.
“Some cooler weather, along with some chilly nights, are likely as we move towards the weekend.”