ANCHORAGE, Alaska -- A U.S. Coast Guard flight over a Shell drilling rig that ran aground off a small Alaskan island found no signs of a fuel spill, officials said Tuesday, but they had to wait until daylight to better assess its impact on the environment.

The Kulluk grounded Monday night on rocks off Sitkalidak Island, an uninhabited island in the Gulf of Alaska.

The storm that has caused problems for Shell's efforts to move the drill into place near Kodiak Island was expected to continue Tuesday, said Darci Sinclair, a spokeswoman for a command centre run by the Coast Guard, Royal Dutch Shell PLC and others.

U.S. Rep. Ed Markey, the top Democrat on the Natural Resources Committee, issued a statement expressing his concerns.

"Oil companies keep saying they can conquer the Arctic, but the Arctic keeps disagreeing with the oil companies," Markey said. "Drilling expansion could prove disastrous for this sensitive environment."

The Kulluk was being towed by two vessels while trying to escape the worst of the storm, but the drill ship was separated offshore from one of the vessels and grounding was inevitable, Coast Guard Cmdr. Shane Montoya told reporters.

The Coast Guard planned to fly out early Tuesday to plan a salvage operation and possible spill response.

The Shell rig was carrying 150,000 gallons of diesel and about 12,000 gallons of lube oil and hydraulic fluid, Montoya said.

Susan Childs, Shell's on-scene co-ordinator, said it was too early to know how the vessel would react to the pounding of the storm. She was optimistic about its salvage prospects and chances for staying intact.

The Kulluk is designed for extended drilling in Arctic waters and underwent $292 million in technical upgrades since 2006 to prepare for Alaska offshore exploration. The drill ship worked during the short 2012 open water season off Alaska's north coast. Its ice-reinforced, funnel-shape hull can deflect moving ice downward and break it into pieces.

When disconnected from a well, it's designed to handle seas to 40 feet (12 metres). Garth Pulkkinen of Noble Corp., the operator of the drill ship, said it was never in danger of capsizing.

With bad weather predicted, the Kulluk's crew was evacuated Saturday.