SAN FRANCISCO (AP) — A fire at one of the country's largest refineries has sent scores of residents to San Francisco Bay area hospitals with breathing problems.

A fire at the Chevron refinery in Richmond broke out late Monday, spewing black smoke over communities about 10 miles northeast of San Francisco.

In neighboring San Pablo, Doctors Medical Center reports about 200 people had arrived with problems breathing and that more patients were arriving early Tuesday.

Kaiser's Richmond Medical Center says several dozen people came to the emergency room complaining of shortness of breath, but none was seriously ill.

Contra Costa County health officials are warning residents to stay indoors. Health official Randy Sawyer says the byproducts in the smoke could be toxic.

Chevron says one employee suffered a minor injury in the fire.