Trains between East Boldon and South Hylton were knocked out by a points failure earlier this afternoon.
Trains are now running into Sunderland, but the Metro service is suspended between Park Lane and South Hylton.
A replacement bus operated by Kingsley's Coaches is now calling at all affected stations.
Metro bosses have apologised for the inconvenience caused.
Met Office announces yellow weather warning for thunderstorms across North East following heatwave
South Shields man jailed for terrifying physical and sexual assault on woman in her own home
Pair set up cannabis farm in town centre flat
Campaigners rally against Local Plan after farmland in Cleadon earmarked for 156 homes
Sea fret - a look at the foggy phenomenon which spoils sunny days in South Shields
Other rail services on the line are also facing disruption.
The latest update states: "We currently have a service suspension between Park Lane and South Hylton in both directions, with a replacement bus service in operation.
"There may be some delays from Park Lane to Airport due to this, and we apologise for any inconvenience caused."