There is a gap in service on the Metro system this morning due to a "lack of available trains".
The service said it is affecting trains between South Hylton in Sunderland and Newcastle Airport.
Bosses have apologised for the disruption.
The service tweeted: "There is a gap in service to trains between South Hylton and the airport due to lack of available trains.
"Sorry for any inconvenience caused.
"Please leave extra time for your journey."
There are also delays of up to 15 minutes between Pelaw and the airport.
Metro tweeted: "Delays of up to 15 mins to trains running between Pelaw and Airport due to a train being withdrawn from service."