ANCHORAGE, Alaska (AP) — Three people were treated for inhalation of ammonia vapors leaking from a Seattle-based fishing vessel as it was docked in Alaska's Dutch Harbor, responders said Sunday.

The leak is believed to be coming from a tank holding up to 5,000 pounds of ammonia, said Coast Guard Lt. Jim Fothergill. The entire cooling system on the 353-foot Excellence contains 20,500 pounds of ammonia.

"It evaporates quickly once it hits the air, but the leak is fairly slow," Fothergill said.

The three people treated for inhalation of the vapors were on board the vessel. Two of them were transported in stable condition for further treatment in Anchorage, according to the Alaska Department of Environmental Conservation. One person has been released, and the other is in good condition but remains under observation, the department said.

The Coast Guard said the leak poses no danger to the public.

The leak began Friday and prompted the evacuation of all 129 crewmembers from the catcher-processor vessel in Dutch Harbor, almost 800 miles southwest of Anchorage. The ammonia is used in a coolant system to flash-freeze the fish.

The vessel was towed Saturday night six miles to Wide Bay, the Coast Guard said.

While the Excellence was docked at Dutch Harbor, firefighters set up a 500-foot exclusion zone around the vessel and sprayed it down with water to reduce fumes wafting out of the vessel. Officials said responders were unable to safely investigate the leak at this point.

Representatives of various agencies set up an incident command.

A hazardous materials team went on board the vessel Saturday and Sunday, measuring high levels of ammonia, which indicated the ammonia was still leaking, responders said.

Fothergill said the ammonia vapors created a thick fog in the spill area.

He said it would be a couple days before the cause and source of the leak can be investigated because the ammonia spill continues. In the meantime, the hazardous materials team is inspecting the Excellence twice a day, he said.