HONOLULU -- The governor of Hawaii has issued a disaster declaration for the entire state after a strong earthquake hit the islands.

In the declaration, Gov. Linda Lingle said the earthquake has caused damage to buildings and public and private roads throughout the state.

The U.S. Geological Survey puts the quake's magnitude at 6.6. There have been several strong aftershocks.

The state Civil Defense has unconfirmed reports of injuries, but communication problems are preventing more definite reports.

The National Earthquake Information Center said there's no risk of a Pacific-wide tsunami, but there is a possibility of significant wave activity in Hawaii.

The quake caused widespread power outages, and phone communication was possible, but difficult. By mid-day, power was restored to Hilo on the Big Island and was starting to be restored to Maui.

The quake happened at 7:07 a.m. off the Waikoloa coast on the Big Island, according to scientists at the Pacific Tsunami Warning Center.

Kona apparently took the brunt of the quake. Kona Community Hospital reported structural damage and multiple landslides were reported on the Hamakua Highway, officials said. Officials are concerned about the structural integrity of the hospital. Crews are evacuating patients to be safe.

Workers are also evacuating patients from the Honokaa Longterm Care Facility.

Officials said that boulders litter several main highways.

A scientist at the Pacific Tsunami Warning Center said he believed this was the largest earthquake in Hawaii since 1983.

"It was an unusually large magnitude and in an unusual location," one scientist said.

Residents reported feeling the shaking for more than a minute in some places. Residents in Niu Valley said the quake made items fall off shelves.

The quake knocked out power to all of Oahu. A Hawaiian Electric Co. spokesman said that the power would be restored over 10 to 12 hours on Oahu.

Power outages have been reported across the islands.

On Oahu, 95 percent of customers have been without power. Authorities say people have been trapped in elevators.