Two chimpanzees broke free from their cage at a California animal sanctuary Thursday, chewing off most of a 62-year-old man's face and biting his wife.

The couple, St. James and LaDonna Davis, had been visiting their former pet chimp Moe at the Animal Haven Ranch. Moe had been removed from their Los Angeles home in 1999 for aggressive behaviour.

The couple, who had brought a birthday cake to Moe, were standing outside his cage when two other chimps in an adjoining cage, Buddy and Ollie, attacked.

Sanctuary officials say they don't know how Buddy and Ollie escaped from their cage.

Hospital officials say St. James Davis is in critical condition with massive injuries to his face, arm and leg. His testicles and a foot were severed and he will require extensive surgery to re-attach his nose.

His wife, LaDonna, was bitten on the hand while trying to save her husband.

The son-in-law of the sanctuary owner shot and killed Buddy and Ollie.

Two other female chimps in the cage with them also escaped, but were captured five hours later and returned to the enclosure.