The incident happened just after 12 p.m. at Creative Nail & Spa, located in the 3000 block of Bristol Street. A 36-year-old Asian man walked inside, doused himself in flammable liquid and set himself on fire, police say.
Another man inside the salon put out the flames with a fire extinguisher. Costa Mesa police responded to the scene with paramedics. The man was taken to Western Medical Center with third-degree burns, according to police. He is listed in critical condition.
There has been no word on a motive, but police say the man's estranged wife works at the salon. She was present at the time of the incident.
One witness said she was having her nails done by the man's estranged wife, who is reportedly the salon manager, when the man entered and appeared distraught. He began yelling at his estranged wife in Vietnamese before setting himself aflame.
No one else inside the salon was injured, and the salon sustained minor property damage.
According to the witness, the estranged couple has three children together.
The Associated Press contributed to this report.