Investigators descended on the Port Newark/Elizabeth Marine Terminal this afternoon after officials received reports of radioactivity emanating from a shipping container.

A Port Authority official said the container was filled with recycled paper, and a metal wire that bound the paper was the source of a positive reading for Caesium-137, a radioactive isotope formed during nuclear fission.

Emergency personnel converged on the North Avenue terminal about 2 p.m. after U.S. Customs and Border Protection officials measured abnormal amounts of radiation coming from the container.

Personnel from federal, state and local agencies, including the FBI, the Port Authority of New York and New Jersey, Union County and Elizabeth were on site for about two hours after the high readings were recorded.

“After review and confirmation from (Customs and Border Protection) Laboratories & Scientific Services (LSS) and in conjunction with our federal, state, and local partners, the container was deemed safe,” the Customs agency said in a statement.

For more than an hour before that, trucks bearing containers trying to get in to the port were at a near standstill along Corbin Road, with some parked along the shoulder waiting to get into Maher Terminals, which had been locked down while authorities determined the cargo’s content.

Juan Rolon, president of the Port Drivers Federation, an independent truckers group, said the lockdown cost truckers countless dollars in down time for which they don’t get paid.

Customs officials took control of the container and were moving it to a secure location, the statement said.