A major oil spill off the coast of southern California has fouled popular beaches and killed wildlife while crews scrambled to contain the crude before it spread further into protected wetlands.

At least 476,000 litres of oil spilled into the waters off Orange County, according to a statement from the city of Huntington Beach.

“The spill has significantly affected Huntington Beach, with substantial ecological impacts occurring at the beach and at the Huntington Beach Wetlands,” the statement said.

The Los Angeles Times reported that birds and fish have been killed. Crews led by the US Coast Guard deployed skimmers and floating barriers known as booms to try to stop further incursion into the wetlands and the Bolsa Chica Ecological Reserve.

The coastline was closed from the Huntington Beach Pier nearly four miles south to the Santa Ana River jetty.

Officials cancelled the final day of the annual Pacific Air Show that typically draws thousands of spectators to Huntington Beach, a city of 199,000 residents about 30 miles south of downtown Los Angeles.

The Times said the oil slick is believed to have originated from a pipeline leak.

The Huntington Beach statement said “while the leak has not been completely stopped, preliminary patching has been completed to repair the oil spill site”, with additional repairs planned.

The spill comes three decades after a massive oil leak hit the same stretch of Orange County coast. On February 7 1990, the oil tanker American Trader ran over its anchor off Huntington Beach, spilling nearly 1.6 million litres of crude. Fish and about 3,400 birds were killed.

In 2015, a ruptured pipeline north of Santa Barbara sent 541,000 litres of crude oil gushing onto Refugio State Beach.

At a news conference on Saturday night, Orange County officials expressed concern about the environmental impacts of the spill and hoped crews could stop the oil before it flowed into sensitive wetlands.

“We’ve been working with our federal, state and county partners to mitigate the impact that could be a potential ecological disaster,” Huntington Beach mayor, Kim Carr, said.

Huntington State Beach is home to a number of species of birds, including gulls, willet, long-billed fletcher, elegant teens and reddish egret, which are a rarity on the west coast, according to Ben Smith, a biologist and environmental consultant for Orange County.

Smith drove to the beach on Sunday to observe wildlife ahead of a construction project planned at the mouth of the Santa Ana River, which flows into the ocean at the border of Huntington State Beach and Newport Beach.

“There’s tar everywhere,” he told the Los Angeles Times. “You think by now we would have figured out how to keep this kind of thing from happening, but I guess not.”