The governor of California has declared an emergency as crews scramble to contain an oil slick and clean up popular beaches after a pipeline rupture dumped thousands of gallons of oil into the ocean.

A day after the spill near Santa Barbara, northwest of Los Angeles, the US Coast Guard said helicopter overflights had shown the slick stretched about 14 kilometres along the Pacific Ocean coast.

The spill caused Governor Edmund Brown to declare an emergency in the Santa Barbara area on Wednesday so as to “quickly” send specialised teams to clean up the hazardous leak.

• California oil pipeline leaks into ocean

“We will do everything necessary to protect California’s coastline,” Brown said in a statement alongside the emergency proclamation.

Teams of white-clad workers used rakes, trucks and pads to scoop up thick oil covering the sand on Refugio Beach, where a campground was evacuated.

A number of government environmental clean-up crews have been mobilised to survey and test the area by aircraft and boat.

The spill was estimated at up to 400,000 litres, of which about 79,500 litres of crude oil may have leaked into the ocean, according to an official update on Wednesday afternoon.

Santa Barbara area beaches would normally be preparing to host thousands of visitors for the upcoming Memorial Day weekend, but the affected area was out of bounds.

A nearby beach has been closed for at least a week and a fishing ban has been imposed by authorities one mile east and west of the spill site.

About 21,000 gallons spilled from an abandoned pipeline on the land near the beach. Photo: Getty

The leak – which began around midday on Tuesday – was caused by a Plains All American Pipeline, the company said.

It said the oil reached the ocean through a drain which has now been blocked off, and “no additional oil is reaching the water”.

Environmental groups warned of the possible long-term impact of the spill.

The Environmental Defense Center lamented the spill, saying there were likely failings that allowed it to occur.

“There continues to be a number of questions … including why there was no automatic shut-off on this relatively new pipeline, and why the early response was not more successful in halting the flow,” said the group’s head, Owen Bailey.

“This region is home to an incredible diversity of wildlife, including numerous species of endangered whales and iconic coastlands that bring people from across the world to visit.”

Kathryn Phillips, California director of environmental group Sierra Club, added: “Every time we hear about an oil spill, we hold our breath and hope it won’t get worse.”

The 61-centimetre pipeline transports crude oil from a nearby above-ground oil storage facility to refineries throughout southern California.

-AAP