Newport Beach firefighters Wednesday were battling a blaze at a mansion in the Big Canyon area.
The fire broke out just after 4 p.m. at 2 Rue Villars, a city official said.
Firefighters switched from an offensive attack to a defensive posture as the roof began sagging and there was a partial collapse of it, said Newport Beach Fire Department spokeswoman Natalie May.
There were no immediate reports of injury, May said. It is expected the home will be red-tagged, she said.
Video from the scene showed flames tearing through a large hilltop home.