A U.S. Coast Guard plane is searching for a Canadian barge that has been drifting in heavy seas for days off the coast of Alaska.

"It's airborne right now en route to the Alaskan Arctic slope to try and relocate the drifting Canadian barge," U.S. Coast Guard Cdr. Shawn Decker said Friday.

Environmentalists say the situation is an example of why the Arctic needs tough regulations for shippers and a strong emergency response capability.

Decker said the barge was last seen on Wednesday and is thought to be within 15 kilometres of the low, gravelly Alaskan shore.

The barge, owned by Northern Transportation Corp. Ltd., broke free from its tugboat on Monday under unexpectedly heavy seas that featured four-metre waves and 70 km/h winds.

"The storm that came up was unforecasted," said Patrick Schmidt, president of Northern Transportation. "Nobody seemed to see it coming."

The barge was returning to Tuktoyaktuk, N.W.T., after delivering supplies to a remote site along the Canadian coastline. The barge is unloaded, although it is carrying 3,500 litres of light diesel in fuel tanks for its own engines.

Decker said a Canadian government plane set off to look for the barge Thursday but had to turn back due to mechanical problems. The crew of the U.S. plane is using drift projections based on local currents and winds to find the 40-metre craft.

Although winds in the area remain high, a break is expected over the weekend, Schmidt said. If that happens, the company will try to get sailors aboard the unmanned vessel.

"Our intent is to get people on board to bring it in under its own power."

Tugboats in the region have all been docked for the winter. Decker said sea ice is closing in on the barge — both from the shore and from the open ocean to the north.

Schmidt said there's a chance the barge may have to be left locked in the ice over the winter.

In case of an accident, Decker said, nearby Prudhoe Bay is well supplied with spill cleanup equipment. He said barges do come loose occasionally.

But such occurrences are likely to become more common if shipping in the Arctic increases due to melting sea ice and northern resource development, he suggested.

"It is well documented that the entire Canadian and American Arctic region is seeing a definite increase in maritime traffic. Any time you have an increase in maritime traffic, you're going to have an increased chance that these incidents are going to occur."

Kevin Harun of the non-governmental organization Pacific Environment pointed out that Arctic weather is routinely unpredictable.

"If we can't deal with this barge that's fairly close to civilization, how are we going to deal with a large ship that's carrying something even more dangerous that goes out of control?" he asked.

"It's just an indicator of why we need good rules in place."

The International Maritime Organization gave preliminary approval last week to a new Polar Code, a mandatory set of rules for Arctic shipping. While those rules are an improvement, they still fail to ban substances such as heavy fuel oil, Harun said.

Transport Canada is reviewing the circumstances surrounding the incident, which will include an overview of weather and sea conditions and vessel operations at the time of the incident.

"Should Transport Canada identify non-compliance with marine safety regulations, the department will not hesitate to take immediate action," Glyniss Hutchings, spokeswoman for the North and Prairie region, said in an email late Friday afternoon.

Hutchings said the Canadian aircraft was not recalled on Thursday, rather a flight planned from Inuvik on Friday was cancelled due to a mechanical issue.

She said the aircraft was being repaired, but the U.S. Coast Guard has told Transport Canada that it is no longer needed.

Note to readers: This is a corrected story. An earlier version said the storm was Tuesday.

News from © The Canadian Press, 2014