The Port of Seattle set up a perimeter of nearly half a mile around one of its terminals Wednesday after bomb-sniffing dogs indicated that two containers from Pakistan could contain explosives, but none was found.

Dozens of non-essential personnel were evacuated from Terminal 18, on Harbor Island south of downtown Seattle, a Port of Seattle spokesman said. A bomb squad used explosive charges to cut into the containers and search the contents.

It wasn't immediately clear what prompted the dogs to alert on the containers, but the bomb squad found no explosives or radioactive materials inside, said port spokesman David Schaefer.

Mike Milne, a spokesman for U.S. Customs and Border Protection, said agents had been using a "gamma-ray" device to peer through the containers' steel walls to determine what they contained. Some of the items did not appear to match what was listed on the containers' manifest, Milne said.

That isn't uncommon, Milne said, and the containers were then subjected to bomb-sniffing dogs, per standard procedure. The dogs reacted, and agents tested for hints of radiation before cutting into the containers.

The Port of Seattle bomb squad apparently did not believe there was a chance of causing a larger blast by using the small charges to gain access to the containers, said spokesman Mick Shultz.

"They wouldn't have done it if they thought there was a chance of that," Shultz said.

Shultz said the containers were supposed to contain oily rags, which are often shipped internationally for recycling or use in packaging, but other items were found. Officials continued examining those items Wednesday afternoon.

Nearby businesses were advised to keep their workers indoors during the scare.

Milne said the ship had originated in Hong Kong and made stops in China and Korea before arriving in Seattle on Monday. The containers were from Pakistan, he said.

Terminal 18 covers nearly 200 acres, making it the port's largest container terminal and one of the largest in the nation. It serves more than 20 steamship lines and receives more than 40 vessels each month.

About 70 members of the International Longshore and Warehouse Union — workers who operate loading and unloading machinery and control the flow of containers — were evacuated just before lunch, as were several dozen truck drivers, said Herald Ugles, president of ILWU Local 19.

A spokeswoman for SSA Marine, which operates the terminal, said the company had no comment.