LOS ANGELES — Tens of thousands of people were ordered to leave their homes in California yesterday after a huge chemical tank began leaking, with warnings it might blow up, sending toxic fumes over a heavily populated area

The tank contained 7,000 gallons (26,000 litres) of methyl methacrylate, a volatile and flammable liquid used to make plastics, with firefighters warning the situation was looking grim.

“There are literally two options left,” Incident Commander Craig Covey said.

“The tank fails and spills a total of about 6-7,000 gallons of very bad chemicals into the parking lot in that area or, two, the tank goes into a thermal runaway and blows up, affecting the tanks around them that have fuel or chemicals in them as well.

“We are setting up these evacuations in preparation for these two options: it fails, or it blows up.

“Please follow our requests and orders for evacuations,” he emphasized.

The incident was unfolding in the Garden Grove area of Orange County, southeast of Los Angeles.

Garden Grove Police Chief Amir El-Farra said about 40,000 people were affected by the evacuation order, with several thousand refusing to leave their homes.

Aerial footage filmed by local TV stations showed jets of water being sprayed at the tank, which has a capacity of 34,000 gallons.