China has suspended imports of shellfish from the west coast of the United States -- an unprecedented move that cuts off a $270 million Northwest industry from its biggest export market.

China said it decided to impose the ban after recent shipments of geoduck clams from Northwest waters were found by its own government inspectors to have high levels of arsenic and a toxin that causes paralytic shellfish poisoning.

The restriction took effect last week and China's government says it will continue indefinitely. It applies to clams, oysters and all other two-shelled bivalves harvested from the waters of Washington, Oregon, Alaska and Northern California. U.S. officials think the contaminated clams were harvested in Washington or Alaska. Right now they’re waiting to hear back from Chinese officials for more details that will help them identify the exact source.

State and federal agencies oversee inspection and certification to prevent the shipment of tainted shellfish. Jerry Borchert of the Washington Department of Health said he's never encountered such a ban based on the Chinese government's assertion that these U.S. safeguards failed to screen out contaminated seafood.

“They’ve never done anything like that, where they would not allow shellfish from this entire area based on potentially two areas or maybe just one area. We don’t really know yet,” Borchert said.

The biggest blow could fall to those who farm or harvest the supersized geoduck clams. In the Northwest, they're concentrated in Washington's Puget Sound, where about 5 million pounds of wild geoduck are harvested each year. Aquaculture accounts for an additional 2 million pounds, according to estimates from the Washington Department of Natural Resources.

A barricade around the Chinese consumer market means trouble for those in the Northwest who rely on Asian trade.

“It’s had an incredible impact,” said George Hill, the geoduck harvest coordinator for Puget Sound's Suquamish Tribe. “A couple thousand divers out of work right now.”

The U.S. exported $68 million worth of geoduck clams in 2012 -- most of which came from Puget Sound. Nearly 90 percent of that geoduck went to China.

Geoduck are highly prized in China, where the clams sell for retail prices of $100 to $150 per pound. Although geoduck are harvested year round, demand peaks during the holiday season leading up to the Chinese celebration of the lunar new year -- which falls on Jan. 31 for 2014.

The geoduck (pronounced "GOO-ee-duck") is a the world’s largest burrowing clam. It’s slow-growing, regularly reaching 100 years old and often weighing as much as 10 pounds.

Harvesters are waiting for the National Oceanic and Atmospheric Administration to negotiate with the Chinese government to come to an agreement on how to move forward and reopen shellfish trade. NOAA stopped issuing certification for shellfish exports last Friday.

Officials say the investigation is ongoing but the closure could last for months. While the industry awaits a resolution at the international level, it is adjusting to the new reality.

The Suquamish Tribe is trying to develop other markets in New York, California and locally at seafood markets in Seattle, Hill said.

Bill Dewey, a spokesman for the largest shellfish supplier in Washington said his company, Taylor Shellfish, is looking at other solutions.

"I was just talking to our geoduck manager and he’s got two harvest crews and three beach crews essentially doing makework," Dewey said. "He’s too nice a guy to lay them off during the holidays but there’s only so much you can be charitable about making work for people and eventually you’re going to have to lay them off.”

