An oil tanker maneuvering through ice ran aground on a reef early Friday and spilled an estimated 150,000 barrels of oil near the port of Valez, the Coast Guard said.

The 1,100-foot Exxon Valdez, bound for Long Beach, Calif., went aground on a charted reef just 25 miles from the port of Valdez, traveling through an area where it should not have been, said Chief Mark Peterson of the Coast Guard Marine Safety Office in Valdez.He said the Exxon-owned ship was trying to avoid large chunks of ice known as growlers. The ice was from nearby Columbia Glacier and often can be found in the area at this time of year.

The tanker maneuvered away from the ice and toward Blight Reef and went aground at 12:20 a.m. Alaskan time, he said.

The tanker carried more than 1.2 million barrels of Alaska crude oil and several oil tanks were ruptured, said Petty Officer Ted French of the rescue center in Juneau.