A large oil spill off the California coast has begun washing ashore at Huntington Beach over the weekend after an oil rig pipeline was breached, leaving dead fish and birds strewn on the sand, local and federal officials say.

An estimated 98,420 litres had spread into an oil slick since it was first reported on Saturday morning (local time), according to Katrina Foley, the Orange County supervisor.

“The impact to the environment is irreversible,” she said in a statement.

She said the spill was caused by a breach connected to the Elly oil rig and stretched from the Huntington Beach Pier down to Newport Beach.

Beaches were closed to swimming and a local air show was cancelled.

Officials from the US Coast Guard, working with local and state agencies, flew planes to assess the spill and had hired contractors to clean it up.

-AAP