There has been widespread disruption across several rail operators in south-east England due to signal failures.
The trainlines affected include Thameslink, Southern, and Gatwick Express.
A Network Rail spokesman said: “At 3.04am there was a loss of power with provider UK Power Networks which significantly impacted our Three Bridges Signalling Centre which controls the signalling – the railway’s traffic light system – across the majority of our Sussex route.”
He said signalling was restored at 6.30am but services remained “significantly disrupted”.
The spokesman added: “We’re really sorry to any passengers disrupted this morning and we encourage passengers to check with their train operator before travelling for the latest information and updates.”