KODIAK, ALASKA -- The U.S. Coast Guard has said it responded to a report of an oil spill from one of its own ships off the coast of Alaska.

The Coast Guard said in a statement on Sunday that the 180-foot (55-meter) buoy tender boat started to discharge hydraulic oil on Saturday around 9:40 a.m. in Womens Bay, about 420 miles (675 kilometres) south of Anchorage.

It was not immediately clear how much oil had spilled, but the tank involved has a maximum capacity of 914 gallons (3 kilolitres), officials said.

Crews from the Marine Safety Detachment in Kodiak are working with the Coast Guard Sector Anchorage Incident Management Division to monitor the cleanup, which the Coast Guard said is contracted to Choctaw Defence Services.

Crews at the scene used absorbent pads, deployed a boom system to contain the spread and used a skimmer to pump oil into a vacuum truck.

"Our primary focus is on mitigating potential impacts to the environment," said Petty Officer 2nd Class Joshua Thorne. Thorne is also a pollution responder from Marine Safety Detachment in Kodiak.

The Coast Guard said the source of the spill was identified and secured. An investigation is ongoing.