Hollywood actor Anne Heche has been declared legally dead, one week after she crashed her car into a Los Angeles building, a spokeswoman said Friday.

Heche, 53, had been comatose in hospital with a severe brain injury since the fiery collision on August 5.

Having lost all brain function, she is "legally dead according to California law," though her heart is still beating as her family keeps her body on life support while exploring organ donations, spokeswoman Holly Baird told AFP.

"Today we lost a bright light, a kind and most joyful soul, a loving mother, and a loyal friend," the family said in a joint statement.

"Anne will be deeply missed but she lives on through her beautiful sons, her iconic body of work, and her passionate advocacy.

"Her bravery for always standing in her truth, spreading her message of love and acceptance, will continue to have a lasting impact."

Heche, best known for 1990s movies "Donnie Brasco" and "Six Days, Seven Nights" as well as a high-profile relationship with talk show host Ellen DeGeneres, crashed her car into a two-story house in the Mar Vista neighborhood of Los Angeles.

The violent collision resulted in "structural compromise and... heavy fire" at the scene, according to the Los Angeles Fire Department.

The ensuing blaze took 59 firefighters more than an hour to contain and fully extinguish, the department said.

Local media reported Thursday that preliminary tests of Heche's blood had come back positive for narcotics, though more were needed to ensure the drugs had not been administered in the course of her treatment.

Celebrity gossip outlet TMZ, citing unnamed police sources, said Heche had tested positive for cocaine and fentanyl, with the latter sometimes used for pain relief in clinical settings.

Heche rose to fame with her role on the soap opera "Another World," for which she won a Daytime Emmy in 1991.

She was nominated for a Tony award for her appearance in "Twentieth Century" on Broadway in 2004.

"My brother Atlas and I lost our Mom," Heche's son Homer Laffoon said in a separate statement.

"Hopefully my mom is free from pain and beginning to explore what I like to imagine as her eternal freedom," he wrote.