ANCHORAGE, Alaska — A powerful earthquake shook a large swath of Alaska Thursday morning, knocking things off shelves and causing people to take cover but bringing no immediate reports of injuries or major damage.

The quake had a preliminary magnitude of 6.2, and it hit at 9:51 a.m. The epicenter was about 80 miles northwest of the state’s largest city, where it was strongly felt, the Alaska Earthquake Center said.

The quake lingered for at least a minute in some areas.

The earthquake center is in Fairbanks, 250 miles northeast of the epicenter, but it was felt, even there, said Sara Meyer, a center research technician.

“It was about 15 seconds of long-period shaking, sort of like you’re on a boat,” Meyer said.

Staffers at the Nesbett Courthouse in downtown Anchorage felt the shaking in their office on the top floor of the six-story building.

“My computer tower fell off my desk,” judicial assistant Ellen Bozzini said. Everyone stood in doorways until an evacuation was ordered. Then they took the stairs outside, where they waited for about 20 minutes before being allowed back in the building.

The fact that the earthquake’s center was, according to the U.S. Geological Survey, about 63 miles underground softened its impact on the state, experts said.