Police are attending a shooting at a social services facility for disabled people in California, the BBC reports.

Fire officials in San Bernardino said it was responding to a “20 victim shooting incident” and it was working to clear the scene.

ABC News reports that there are 12 people dead but police have not confirmed that number.

It is still a “very active scene” and police are trying to secure the building, said a police spokeswoman.

There may be up to three gunmen, she said, and they were heavily armed and possibly wearing body armour.