LAS VEGAS -- Crews were working to restore power after a surge shut off the exterior lights of three Strip hotels-casinos, casino officials said.

Shortly before 8 p.m. Tuesday, a surge shut off the exterior lights of the Luxor, Excalibur and Mandalay Bay casinos, fire officials said. The Four Seasons Hotel may also be affected, they added.

While officials said the exterior lights are the only ones affected, guests have called KVVU FOX5 News to report that some hotel rooms were dark and that common areas were running on backup power sources.

The cause of the surge was unknown as of late Tuesday night, power crews said. They are working to repair the damage, but they do not know how long it will take to repair.