ANCHORAGE, Alaska — Back-to-back earthquakes measuring 7.0 and 5.7 shattered highways and rocked buildings Friday in Anchorage, sending people running into the streets and briefly triggering a warning to residents in Kodiak to flee to higher ground for fear of a tsunami.

The warning was lifted without incident a short time later. There were no immediate reports of any deaths or serious injuries.

The U.S. Geological Survey said the first and more powerful quake was centered about 7 miles north of Anchorage, Alaska’s largest city, with a population of about 300,000. People ran from their offices or took cover under desks.

“We just hung onto each other. You couldn’t even stand,” said Sheila Bailey, who was working at a high school cafeteria in Palmer when the quake struck. “It sounded and felt like the school was breaking apart.”

A large section of an off-ramp near the Anchorage airport collapsed, marooning a car on a narrow island of pavement surrounded by deep chasms in the concrete. Several cars crashed at a major intersection in Wasilla, north of Anchorage, during the shaking.

Anchorage police Chief Justin Doll said he had been told that parts of Glenn Highway, a scenic route that runs northeast out of the city past farms, mountains and glaciers, had “completely disappeared.”

The quake broke store windows, opened cracks in a two-story building downtown and disrupted electrical service.