Heche, 53, was taken to hospital on Friday with severe burns after she smashed her car into a home in the Mar Vista area of the city, which then caught fire.
“Despite previous reports that Heche was stable, shortly after the accident, Anne Heche became unconscious, slipping into a coma and is in critical condition,” her representative told ABC News.
“She has a significant pulmonary injury requiring mechanical ventilation and burns that require surgical intervention.”
The latest update on the actor’s condition came after it emerged that she is under investigation for DUI, as well as hit and run for the accident, that happened when her car left the road at a T-junction, police say.
Los Angeles Police Department investigators obtained a warrant for a blood draw on the day of the incident, and are still waiting for the results to come back, according to CNN.
Once LAPD has the results and the investigation is complete, the case will be referred to the LA City Attorney’s office which will make any decision on charges and prosecution, LAPD Officer Annie Hernandez told the news network.
Previously her representatives had described Heche as being in a “stable” condition in a hospital in the city.
“Anne is currently in stable condition,” her representative had said in a statement on Saturday, the day after the incident. “Her family and friends ask for your thoughts and prayers and to respect her privacy during this difficult time.”
LAPD said that the actor appeared to be under the influence at the time of the accident and acting erratically. The blood draw results could take weeks to be returned to investigators, according to TMZ.
No one else was injured in the incident and no arrests have been made in the case, which is still under investigation.
Heche was taken from the scene of the accident in an ambulance and hospitalised with serious injuries, according to Los Angeles Fire Department.
The fire at the scene that it took 59 firefighters one hour to put it out.