Eight cable bonds have been stolen from the tracks in the East Boldon area on Tuesday afternoon (July 21).
Repairs were expected to take up to two hours but Tyne and Wear Metro has confirmed that service has resumed.
It follows an attempt by thieves to steal cables from the Metro line at Jarrow this morning – although damage there was less severe.
The service between Heworth and Sunderland was suspended this afternoon while Network Rail carried out repairs.
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A Nexus spokesperson said: “Cable bonds have been stolen from the Metro line in the East Boldon area. This resulted in a suspension of services between Pelaw and St Peter’s.
“This section of line is a shared piece of infrastructure that serves Metro, rail and freight services through Sunderland. It is owned and managed by Network Rail.
“This follows on from an attempt to steal cables from the Metro line at Jarrow this morning, although the damage there was less severe.
“These offences have been reported to the police.
“Cable theft causes huge disruption to our customers. It is also dangerous to tamper with trackside equipment which has high voltage power running through it.
"Thieves are risking their lives by doing this.”
Anyone with any information about the incident is urged to contact Northumbria Police on the ‘Tell us something’ page of the force’s website.