Metro passengers faced delays after a track circuit fault in the Sunderland area this morning.
Services were delayed by up to half an hour between South Hylton and Pelaw as a result of the problem.
The fault was rectified by about 6.30am, but delays have still been reported since then.
An initial tweet by Metro said: "Delays of up to 20 minutes between Pelaw and South Hylton, and up to 30 minutes between South Hylton and Pelaw due to a technical fault."
The service later updated: "The earlier fault in the Sunderland area has been fixed.
"There are still some delays but trains are frequent and running to all destinations."
It was later confirmed that there would be a 'gap in service' between the two stations.
Metro tweeted: "There will be a gap in service between Pelaw and South Hylton.
"The 7.23am South Hylton to Airport is the train affected. Apologies."