Authorities set up a half-mile (800-meter) perimeter around a terminal at the city's port Wednesday after bomb-sniffing dogs indicated that at least one container recently unloaded from a ship could contain explosives.
Dozens of personnel were evacuated from Terminal 18, south of downtown. A bomb squad was set to examine the container and determine its contents.
The container was taken off the ship because of questions about a manifest, port spokesman David Schaefer said.
"The bomb-sniffing dogs did what bomb-sniffing dogs do, and it caused us to be worried there might be explosives," Schaefer said.
Coast Guard Petty Officer Mike Zolzer said the container was supposed to contain oily rags, but authorities apparently found items that did not match that description.
Zolzer said he did not know where the ship originated.
Terminal 18 covers nearly 200 acres (80 hectares), making it the port's largest container terminal and one of the largest in the US It serves more than 20 steamship lines and receives more than 40 vessels each month.