SAN FRANCISCO - A powerful earthquake and repeated aftershocks rattled Hawaii on Sunday, knocking out power and unnerving residents and vacationers but causing no injuries or extensive structural damage, agencies reported.

People wait in line for food at a roadside chicken stand in Kihei, Hawaii, Sunday, Oct. 15, 2006, after an earthquake struck the big island of Hawaii knocking out power and forcing restaurants and other merchants to close. [AP]

The 6.6 magnitude earthquake struck off the west coast of Hawaii on Sunday morning, with shaking and power outages felt as far as 150 miles (240 km) away on the island of Oahu.

The earthquake was not strong enough to trigger a tsunami warning, according to Victor Sardina, a geophysicist at the Pacific Tsunami Warning Center.

There were no immediate reports of injuries or fatalities as the earthquake struck off a sparsely populated area, but there were scattered reports of damage. Power outages were widespread, including in Honolulu and across Oahu, where most of the state's residents live.

Gov. Linda Lingle declared a state of emergency, allowing her to mobilize the state's National Guard units, said Ray Lovell, a spokesman for Hawaii State Civil Defense.

"It's going to take a while to get the power back on (on Oahu) because the grid is so massive compared to any of the other islands," Lovell said.

The U.S. Geological Survey considers an earthquake of 6.6 magnitude to be strong. The agency initially recorded the earthquake as a 6.3 magnitude temblor.

The Honolulu Advertiser reported on its Web site that Honolulu International Airport was closed, there were landslides in Hamakua and Kealakekua, and major damage at Kona Hospital, the Honokaa Long-term Care Facility and the Royal Kona Resort.

"It was the biggest earthquake we've been through. It was pretty serious and we've lived in Tokyo for 11 years," said Arthur Roberts, who lives 15 miles (24 km) north of Hilo on Hawaii. Japan has severe earthquakes.

Honolulu resident Carol Chesney said the earthquake shook the city enough to awaken everyone. "The whole house really rattled," she told Reuters by telephone.

Stuart Koyanagi, another geophysicist at the tsunami warning center, said the 6.6 magnitude earthquake was followed seven minutes later by a 5.8 magnitude temblor and by several smaller quakes. Seismologists warned of aftershocks through Monday.

Michael Poland, a geophysicist with the U.S. Geological Survey's Hawaiian Volcano Observatory, said the earthquake was likely the largest to hit Hawaii since 1989, and possibly the largest since an even larger one measuring 7.2 hit in 1975. Those earthquakes struck less developed areas, Poland said.