Officials have halted cargo movement at the Port of Long Beach after a World War II-era explosive device was found in the ground during construction Wednesday morning, authorities said.

A safety perimeter was established around the area, and a bomb squad has been called to the scene, according to a statement from Lee Peterson, spokesman for the Port.

It wasn’t immediately clear whether the device posed a threat. “A U.S. Marine Corps is present to advise and assist,” the statement said.

Several agencies are assisting, including the Los Angeles County Sheriffs Department and the Long Beach Police Department.

The device was found at Pier G, near the southern edge of the Port complex.

The Port complex formerly housed a major U.S. Navy base, home to several battleships and support ships, two aircraft carriers and a large Naval landing. The base operated here from 1919 to 1997.

When it closed, the Port of Long Beach acquired the land and developed it into one of the world’s largest container terminals. The complex includes a total of six terminals.