A tanker being loaded with fuel broke free of the dock in Nikiski and ran aground, the U.S. Coast Guard said Thursday.

The 575-foot Seabulk Pride was moored in Nikiski on the Kenai Peninsula overnight when it broke free of the dock, said Petty Officer Steve Harrison with the Coast Guard's command center in Juneau. Nikiski is 80 miles south of Anchorage.

Harrison said the Coast Guard received the report at about 6 a.m. Tugs were on the way to the scene to rescue the ship, he said.

The Seabulk was struck by an ice flow and broke free from its moorings at 5:25 a.m., said Sarah Simpson, a spokeswoman for Tesoro in San Antonio. Tesoro has a refinery in Nikiski. The tanker was being loaded with product when it broke free, she said.

Some of the product, described as heavy vacuum gas oil and unleaded gasoline, was released into Cook Inlet. Simpson said it was not known how much fuel leaked into the water when the ship was hit by ice and broke free.

Harrison said the tanker drifted and made a soft landing.

"The tanker is aground on silt," Harrison said, adding that that was "a good thing."

The tugs were expected to arrive at about 11 a.m.

The Seabulk was tied to the dock when it broke free, Harrison said. He said an early report indicated that there may have been ice buildup that lifted the boat and strained the lines, eventually separating the ropes, he said.

"When the ice builds up, you get overflow and overlap. It will strain the ropes when the tide comes in," he said.

There were no reports of injuries.

According to the company's Web site, the Seabulk Pride is a double-hulled petroleum tanker with a carrying capacity of 342,000 barrels of oil. It is owned by Seabulk Tankers, Inc., of Fort Lauderdale, Fla.

The Coast Guard said two tugs that help ships on and off the dock were helping the stranded tanker. Anderson Tug & Barge in Anchorage also was sending a tug and Seabulk was sending an oil service vessel from Homer.