A power surge on the Tyne and Wear Metro service brought trains to a standstill, and caused a station evacuation earlier today.
Monument Metro Station, in Newcastle City Centre, was evacuated earlier as a "precaution" following a power surge on the line, Nexus have confirmed.
The station has now re-opened, and the service has resumed system-wide, apart from between South Gosforth, where the fault occurred, and Shiremoor.
Trains were on hold across the service earlier today while the fault was investigated.
A Nexus spokesman said: "There was a large power surge in the area.
"That is still under investigation. Monument was evacuated as a precaution.
"We are advising passengers to seek alternative transportation until we solve what the problem was.
"It affects a very large area of the system, not just the city centre. All trains are on hold throughout the system."
Five fire crews from Newcastle Central, Gosforth and Gateshead attended Monument Metro Station to work with Nexus staff to lead 71 passengers and the driver on a train stuck in the tunnel to safety above ground.
Officers from Northumbria Police attended Newcastle city centre to reassure and direct the public.
An investigation is now underway to determine the cause of the problem.
Metro tickets are being accepted on Arriva, Go North East and Stagecoach buses while the delays continue. It is expected that they will continue throughout the afternoon and this evening.
Steven Bourke, 29, became stuck at Brockley Whins station after having to leave a train.
He said: "There's a huge crowd and most are on the platform.
"Most have been keeping up to date on their phones, but nobody really knows what is going on.
"Metro said on their Twitter that tickets could be used on the buses, but Go North East are not accepting them.
"We have seen trains going towards Sunderland but none going the opposite way."