An alert that Nevada had been rocked by a 5.9 magnitude earthquake early Thursday sent phones buzzing briefly before the U.S. Geological Survey quickly deleted the warning from its webpage and said it had been sent in error.

“The event did not occur, and has been deleted from USGS websites and data feeds. The USGS is working to understand the cause of the false alert,” the agency said.

The alert for what would have been one of the largest earthquakes in the United States this year set off a chain of automatic warnings as far away as the San Francisco Bay Area as people in Dayton and nearby Reno began to report that they had felt no shaking.

It was unclear what prompted the false alert, which said the earthquake had occurred at 8:06 a.m. local time. Within minutes, some news outlets publ

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