Around 25 racehorses are known to have been killed and many others are missing after a wildfire swept through a training centre in north east San Diego County.

The California Horse Racing Board says nearly 500 horses were stabled at the San Luis Rey training centre when the fire erupted amid strong Santa Ana winds on Thursday ((Friday AEDT).

The board says workers risked their lives to free horses from stalls and herd them into safer areas with two trainers also hurt.

Bloodhorse.com said Martine Bellocque suffered second and third degree burns to 50 per cent of her body as she tried to rescue her horses while Joe Herrick was also hospitalised with serious burns .

When it was safe for vans to enter, surviving horses were transported to the Del Mar racetrack which is accommodating several hundred horses being cared for by staff and volunteers.