An oil rig that ran aground in Alaska on New Year's Eve in "near hurricane" conditions dragged two vessels trying to control it more than 10 miles (16 km) toward a wave-battered rocky shore before the crews cut it loose to save themselves.

The stricken Kulluk oil rig is owned by Royal Dutch/Shell and is a vital part of its controversial Arctic oil drilling program, which has encountered several problems.

The 28,000-tonne, saucer-shaped rig was pushed toward the shore by waves up to 35 feet (11 meters) and winds up to 62 mph (100 kph), dragging its main towing vessel the Aiviq and a tug, the Alert, behind it.

"We are talking about near hurricane-strength conditions," said Darci Sinclair of the Kulluk Tow Incident Unified Command, set up by the U.S. Coast Guard and the companies involved.

The unified command said the Kulluk was now "upright and stable" on Sitkalidak Island in the Gulf of Alaska. Salvage experts spent three hours aboard it Wednesday for a structural assessment to be used by Netherlands-based Smit Salvage.

They saw no sign that the fuel tanks had been breached. It was still too early to give a recovery timeline, said a Coast Guard official, ahead of a more detailed update on Thursday.

Smit had worked on the Selendang Ayu, a ship that broke in half and spilled fuel and soybeans after grounding in bad weather off Unalaska Island in December 2004. Smit also worked on the Costa Concordia, which grounded off Italy last year.

More than 600 people are involved in the Kulluk response.

"It is important that the American public and our elected officials understand the dangerous and difficult challenges being faced by the response crews," Rear Admiral Thomas Ostebo, commander of the Coast Guard in Alaska, said in the statement.

The 30-year-old Kulluk is operated by Noble Corp and was refitted by Shell for its summer 2012 drilling expedition in the Beaufort Sea off northern Alaska.

Shell spent $4.5 billion preparing for extraction activities there and in the Chukchi Sea further east, but has yet to complete a single well.

Headlines that raise questions about the wisdom of drilling so far north in such an environmentally delicate and technically challenging place were not expected so early in 2013, given that activity stopped for the season two months ago.

Any Kulluk damage may threaten Shell's 2013 drilling program because its oil-spill plans require a second rig to be available at all times in case a relief well needs to be drilled to kill a well. The Noble-owned Discoverer is Shell's other Alaska rig.

The Kulluk was on its way south for the winter. It had been towed east from the Beaufort, and then south through the Bering Strait that separates the northernmost U.S. state from Siberia.

The Kulluk's 18-strong crew had already been lifted off when the four-day battle to keep it off the rocks began. (Reuters, edited by Topco)