Train services in and out of London Victoria are being cancelled, diverted or delayed by as much as 30 minutes because of "power supply problems".
The issue appears to be affecting all trains in and out of the station.
The fault, which has been disrupting trains for at least an hour, looks likely to continue into rush hour.
“An estimate for the resumption of normal services will be provided as soon as the problem has been fully assessed,” train operator Southeastern said.
“London Underground are conveying passengers via any reasonable route until further notice. Arrangements have been made for Southeastern rail tickets to be accepted for these journeys.”
Some commuters' trains are being diverted to and from Blackfriars, but commuters are being advised that if their journey is delayed for more than 30 minutes they can claim compensation.
Separately, signalling problems are affecting services through Orpington.