"She is an amazingly talented woman. I love you, Anne, I love you and I think you are such a talented person. I hope everything is OK, I hope you come through this. My heart goes out to you.
"I'm sorry you had this tragic thing happen to you, and I'm sending you all my love. Everyone please join me please in sending their support and love to the wonderful Anne Heche. Thanks."
Actress Rosanna Arquette, 62, tweeted: "Anne Heche is in hospital severely burned from a car accident. This is really tragic. Pray for her."
Their messages have provoked outrage online as they come amid speculation that Heche was drunk at the wheel, with many critics highlighting she could have killed people in her crash.
It comes as Heche's 'Big Little Lies' actor ex-boyfriend James Tupper, 57, who dated her for 10 years and shares a 13-year-old son with the actress, also posted about the accident on Instagram, saying he and their boy were hoping she has a quick recovery.
He said: "Thoughts and prayers for this lovely woman, actress and mother tonight, we love you."
Heche, who also has son Homer with her 48-year-old cameraman ex-husband Coleman Luffoon, smashed her car into a Mar Vista home at 90mph, causing the house to burn down.
She had earlier been pictured with what appeared to be a bottle of vodka in the cupholder of her Mini Clubman, and had spoken about drinking the spirit with wine chasers in an episode of her podcast released hours before the fiery smash.