Mesa police officers at the Vegas music festival where shots rang out Sunday night are all accounted for, the Mesa Police Department said.

The department confirmed Monday morning it had a group of off-duty officers attending the festival as regular concertgoers.

Mesa police said the officers are OK.

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"We are happy to report no fatalities on our end," a department spokesperson said.

A gunman opened fire killing at least 50, wounding 400 more and prompting chaos as thousands of concertgoers jamming the Las Vegas Strip scrambled for cover.

It's become the deadliest mass shooting in modern U.S. history.

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