caused at least one landslide on a major roadway on the island of Hawaii, known as the Big Island, according to Hawaii's KITV. Officials said a state of emergency had been declared on the Big Island.

Authorities told KITV they have not received news of any fatalities from the strong quake, which was measured by the National Earthquake Information Center as 6.6 in magnitude. (Watch rocks block roads, damage to buildings -- 2:08 )

"We were rocking and rolling," Anne LaVasseur told The Associated Press.

She felt the quake as she stood on the second floor of her Big Island home.

"I was pretty scared," said LaVasseur. "We were swaying back and forth, like King Kong's pushing your house back and forth." (Watch how people woke up to shaking and quaking -- 1:28 )

Emergency room ceilings collapsed and electricity went out at Kona Community Hospital on the Big Island, which began transporting seriously ill patients and nursing home patients to Hilo Medical Center around 11 a.m. (5 p.m. ET), said spokeswoman Terry Lewis.

No Kona Hospital patients were injured during the quake, Lewis said.

Live footage from KITV showed lines outside grocery stores and crowds growing at gas stations.

Power was restored to Hilo on the Big Island. Power is slowly coming back on throughout Maui, the Hawaii National Guard told The Associated Press.

Officials did not have a firm estimate of how many people were without power. In areas such as Waikiki, which relies heavily on tourism, visitors began lining up outside convenience stores to buy water and other supplies. Managers were letting tourists into the darkened stores one at a time.

Bill Wong, a Big Island resident, said damage to buildings was extensive. He said the 100-foot-tall stack to a century-old sugar mill collapsed into a pile of rubble. "Everything in our house is damaged," he said. "Our whole house was rocking, it was swaying from left to right," he said. He described his neighborhood after the quakes as looking "like a war zone." (Watch the Big Island's mayor describe the damage -- 4:57 )

Bruce Pressgrave of the U.S. Geological Survey said preliminary reports indicated the quake was centered along the west coast of the Big Island, 153 miles southeast of Honolulu, which is on the island of Oahu. There is no threat of a tsunami, the Geological Survey said. (Map)

CNN meteorologist Rob Marciano said an aftershock of 4.2 struck about 10 a.m. (4 p.m. ET). This is normal activity, according to the USGS, but it was the strongest aftershock after a series of at least 10 aftershocks ranging in the 3.0 and lower range.

KITV anchor Shawn Ching said there was "significant" structural damage throughout the Big Island. A spokesperson for a hospital in Waimea said its emergency room is "inundated" with patients who suffered lacerations during the quake.

KITV anchor Mahealani Richardson told CNN the west side of the Big Island is difficult to navigate and has one primary road.

Big Island Mayor Harry Kim said on KITV that he is looking into whether the area is eligible for federal assistance.

Honolulu International Airport canceled departing flights but was still accepting arriving flights. Officials said power outages had led to plumbing problems at the airport, which was creating an unpleasant situation for workers and travelers who continued to arrive at the airport in hopes of catching a flight.

Cell phone reception was sketchy on the islands, officials said.

Residents were urged to stay at home and not use their telephones to avoid tying up emergency lines.

Lingle said she had no report of fatalities but that boulders fell on highways, rock walls collapsed and televisions had been knocked off stands.

The Pacific Tsunami Warning Center said there is no reason to fear a tsunami, but that did not stop some panicked vacationers from heading to the airport in hopes of catching a flight home, said Erik von Ancken, a reporter from Orlando, Florida. He is vacationing in Hawaii with his fiancee.

"We were walking on some of the paths by the ocean," he said. "The fish in the pond started jumping... the windows on the buildings started to shake. People started to run for higher ground... there was a lot of fear."

Home Depot in Honolulu was one of the few stores open. It reported that it was nearly out of batteries, but still had supplies of propane and charcoal. Stewart Weinstein, assistant director of the Pacific Tsunami Center, told CNN the quake's magnitude was below the center's threshold to issue a tsunami warning.

"We've been monitoring our sea-level instruments... so we're confident there's not going to be any tsunami effect from this earthquake," he said. Weinstein said the last time Hawaii had a quake of this magnitude was in 1983.

A U.S. Pacific Command spokesman, based in Hawaii, said that there had been no immediate reports of damage to U.S. military assets in Hawaii. There had been no requests for military assistance from civilian authorities, he said.