Two Metro trains had to be withdrawn from service after vandals smashed windows on them.
The incidents happened in the Meadow Well area of North Tyneside just after 6pm on Sunday.
Two trains were left with a damaged window and they had to be taken off the network.
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As a result, there were delays to services running between Meadow Well, St James and South Shields.
The incidents have been reported to the police and Nexus is working with officers to track down the offenders.
A Nexus spokesperson said: "Two Metro trains were withdrawn from service on Sunday evening after incidents of criminal damage.
"The offences have been reported to the police and we will support them with footage from our CCTV systems to pinpoint the offenders.
"We are working closely with the police to crack down on anti-social behaviour on the network.
"It's a shame when a small minority spoil it for the law abiding majority of people who rely on Metro services.
"Anyone who gets caught damaging a Metro train faces prosecution, a substantial fine and a possible ban from travelling on the network."
