The mayor of Elizabeth confirmed up to five devices were found in a backpack hidden in a trash bin near the Northeast Corridor train track Sunday night.
One of the devices exploded as the FBI worked to disarm it overnight.
There was no immediate report of injuries or damage. A message left with the FBI wasn't immediately returned. The mayor warned that other explosions were expected.
Services were suspended as a result of the discovery.

According to WCBS, businesses in the area were shut down and evacuated as bomb technicians used a robot to investigate the device, believed to be a bomb.
The station reports two scavengers came across the backpack in a dumpster, and noticed it was attached to wires.
They reportedly left the package under the train tracks and ran to police to report the discovery.