Thousands of rail passengers commuting into London faced delays on Thursday after signalling problems near London Bridge.
Blown fuses disrupted journeys into the city from the south and some services were cancelled.
Services on the Brighton Mainline, Metro, Redhill, Mainline West and Mainline East were affected, Southern Railway said.
A spokesman for Network Rail said the problem began at 5.30am when fuses blew at Honor Oak Park station.
He said: "It took a little time for services to get back to normal, but they are running as normal now. There were some diversion routes available."
Chris Hudson, a spokesman for Southern Railway, said: "Network Rail are telling us the problem has been corrected, but because of the time of day it happened and the amount of trains we had going in, although it has been fixed there are residual delays."
Mr Hudson said he expected Southern Railway trains would be affected until about 11.30am.
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