Rush-hour commuters and holidaymakers are facing delays and cancellations after a fire broke out next to railway tracks near a major station.
Southern and Gatwick Express train services are not running to or from London Victoria.
Trains were cancelled after a fire started between Victoria and Clapham Junction, with disruption expected to continue until around 10am, National Rail said.
It comes as British Airways passengers at airports including Gatwick and Heathrow report flight delays and
Southern and Gatwick services will divert to London Bridge where possible with travellers advised to Thameslink or other Southern services where available, it added.
Tickets can be used for alternative transport on London buses, some Thameslink services, and the London Underground.
The cause of the fire was not stated.
Meanwhile a number of flights have been delayed and long queues have been reported by British Airways passengers trying to check in due to "systems problems".
Author David Hewson tweeted a photo while he was stuck in a long queue at the check-in desk at Gatwick.
He wrote: "Major computer failure with British Airways at Gatwick this morning.
"This is the queue for the queue at check in.
"Currently stuck on ground cos pilot can't get data.
"Set off early if you have a flight."
He added: "Stuck on the ground at Gatwick because your systems are down and pilots can't get weight and balance.
"Do you really have no idea how long this will go on?"
A British Airways spokesperson said: "We are experiencing some systems problems this morning which are affecting check-in and flight departures.
"Please check ba.com and manage my booking for the latest flight information and allow extra time at the airport."
