"This incident is all the more reason to ban fracking both offshore and onshore to help prevent future spills and protect Santa Barbara's beautiful beaches and coastal environment," Becca Claassen, a Santa Barbara County organizer with Food & Water Watch, said in an emailed statement.

Sheen reported off the Santa Barbara coast stretches for about 4 miles from a leak of about 500 barrels, or 21,000 gallons, of crude oil from a 24-inch pipeline operated by Plains All American Pipeline, which has headquarters in Texas.

Bob Deans, a spokesman for the Natural Resources Defense Council, said big oil comes with big risks.

"This time, a burst pipeline and its resulting four-mile oil slick remind us yet again: it's time to invest in clean energy," he said in a statement. "We need real solutions that don't spill, explode or cause climate chaos."

California is the third-largest oil producer in the United States. While the U.S. Coast Guard in the region said the source of the spill was secured, there was no information on the origin of the oil spilled from the pipeline.

Plains All American operates crude oil storage depots and pipelines in and around the southern California area. There was no statement on the breach from the pipeline company.

The Coast Guard said it was working with emergency crews, wildlife officials and regional oil companies to respond to the spill. A commercial oil spill company was contracted for cleanup operations.

"The Coast Guard will continue to monitor the situation and conduct an investigation," it said in a statement.