Hawaii is under a tsunami watch after an 8.3-magnitude earthquake off the coast of north Chile.

The Pacific Tsunami Warning Center issued the watch, saying a tsunami may have been generated by Wednesday's earthquake.

If there is a tsunami, the center estimates that the first wave would arrive about 3 a.m. Thursday.

The powerful earthquake shook Chile's capital, causing buildings to sway and people to take refuge in the streets. Several strong aftershocks hit within minutes as tsunami alarms sounded in the nearby port of Valparaiso. There were no immediate reports of injuries, but authorities said some adobe houses collapsed in the inland city of Illapel, about 175 miles (280 kilometers) north of Santiago.

The U.S. Geological Survey initially reported the quake at a preliminary magnitude of 7.9, but it quickly revised the reading upward to 8.3.

A watch means that a tsunami is possible, but it doesn't mean it will happen, said Chevy Chevalier, a meteorologist with the National Weather Service in Honolulu.

"A watch is for everybody to be aware of it, that it's a possibility," he said. "A warning means it's happening right now or it's imminent."

A tsunami warning was last issued for Hawaii in 2012, after a powerful earthquake off the coast of Canada. The Pacific Tsunami Warning Center lifted its tsunami advisory three hours after downgrading from a warning and less than six hours after the waves first hit the islands. The state was spared from severe surges.

The Hawaii Emergency Management Agency said state officials are standing by, awaiting updates from the warning center.

On the Big Island, officials were bracing to be the first island affected, county spokesman Ilihia Gionson said. Officials were gathered Wednesday in the county's emergency operations center in Hilo, he said.

"It's too early to tell," he said. "This early it's best to just stay informed."

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Associated Press Writer Audrey McAvoy contributed to this report.