A report of a pipe bomb shut down the upper level of the George Washington Bridge in both directions for about two hours on Thursday evening before police determined it was not a threat, authorities said.

The suspected pipe bomb was reported to be on the New Jersey side of the bridge soon after 9 p.m., cops said.

Traffic in the area snarled before police determined the pipe found at the scene was not explosive, authorities said.

The pipe had caps on the ends of it, and police are working to find out how it ended up on the bridge, law-enforcement sources said.

Soon after 11 p.m., the New York City Office Emergency Management tweeted that all lanes had reopened.

“Following a prior closure, all lanes of the George Washington Bridge upper level have reopened in The Bronx and Manhattan. Expect residual delays,” it wrote.