The Metro has been suspended between South Shields and Bede after the overhead power line failed.
Trains are expected to be suspended until 7pm while engineers repair the section of overhead line in Chichester.
A Nexus spokesman said: “The overhead line at Chichester has a split in the join. The wire itself is not down but the split needs to be repaired and the wire reset at the required tension.
“The repairs got underway at 3.30pm and are expected to take around three hours.”