LAS VEGAS — A power outage has forced the evacuation of 900 rooms at the Rio casino in Las Vegas, officials said.

The evacuations happened around 7 a.m. Thursday when a fuse blew in a backup generator that was powering the hotel’s Masquerade Tower, said spokesman Richard Broome of the Rio’s parent company, Caesars Entertainment.

The outage affects the fire control systems, so officials are making patrons leave their rooms.

“It all went dark, and then we heard a commotion in the hall,” Amanda Paulsen, who was staying at the casino with her husband for the holiday weekend, told the Las Vegas Review-Journal. “We went to look and someone said, ‘The power’s out, we have to leave.’ ”

Patrons are being directed to the Rock of Ages lounge, where they’re getting food, beverages and updates about the situation, Broome said. It’s too early to say when the power will be restored and whether guests will be compensated for the inconvenience, he said.

The backup generator was on after a small electrical fire Wednesday night compromised the main power source.