The vehicle crashed on Route 21, also known as McCarter Highway, just before 1:45 a.m.
The tanker, which was hauling about 5,000 gallons of gas, burst into flames and sent fire and smoke pluming into the night sky.
Firefighters responded to the scene and poured foam on the flames.
The driver of the tanker was injured and was being treated.
Service on the Northeast Corridor and North Jersey Coast Line was temporarily suspended in both directions due to the fire and police activity near Newark Penn Station. Amtrak was also affected, with problems extending to signals and overhead wires.
Trains were running again within a few hours, but New Jersey Transit spokesman John Durson Jr. says trains on the Northeast Corridor, North Jersey Coast and Raritan Valley lines were operating with residual delays of up to 60 minutes. Systemwide cross-honoring is in effect.
One NJ Transit train was held at Newark's Penn Station and another was held in Raritan, with some 600 passengers bused between the stations.
Police are investigating the accident, but they believe the tanker may have been cut off by another vehicle.