Manhattan, Hermosa and Redondo beaches remained closed Thursday after tar-like globs ranging from the size of golf balls to footballs began washing ashore along a six-mile stretch of coastline.

At least 6.5 miles of Los Angeles County coastline from the El Segundo Jetty to Torrance Beach was shut, and crews worked into the night in an attempt to clean up the mess. The beaches will be closed until further notice, but several surfers could be seen at the beaches Thursday morning.

"We ask that the public not go into the water," said Chris Linkletter, of the Los Angeles County Lifeguard Division. "The source has been undetermined, they're still testing what's washed up."

According to the U.S. Coast Guard, pollution investigators are examining the substance found along the beach, but still do not know exactly where it came from. It's being described as oil or tar globs.

"We are continuing to analyze the beaches and trying to determine the source of the tar balls and tar patties," said Commander Charlene Downey, of the U.S. Coast Guard.

Downey was asked at a Thursday morning news conference whether the substance might be related to an oil spill last week off the coast of Refugio State Beach in Santa Barbara County. She said it's too early to tell whether there's a connection.

"It could be anything," said Downey. "It could be naturally occurring, we just can't tell right now what might be the source.

"I can't tell you right now what specifically that product is. Those analysis and tests take time."

They will be analyzing samples to see if they can pinpoint whether the globs been processed by a company or naturally occurred. The waste is also being collected so the cost of the clean up can be calculated, and if anyone is found responsible they will be billed.

Environmental group Heal the Bay has sent scientists to monitor the cleanup.

"It's very disturbing to see such a large swath of beach covered during the summer high beach going time for an oil incident," the organization's vice president Sarah Sikich said.

Locals did say small tar balls that occur naturally are seen in the area from time to time, though they are not usually so plentiful.

The substance was first reported in the 2200 block of The Strand just before 1 p.m., according to the Los Angeles County Fire Department. A U.S. Coast Guard helicopter flew over the area, but did not find any substance or oil slick in the water.

The substance could be seen dotting the sand in aerial footage taken by NewsChopper 4.

The small balls of substance were described as oil patties or oil balls by Petty Officer Marshal Anderson of the Coast Guard. Anderson said investigators are taking samples of the petroleum-based substance to determine if it is a product or naturally occurring.

There has been no impact to area wildlife, said Sal Garcia, of the California Depart of Fish and Wildlife.

NBC4's Jonathan Lloyd and Toni Guinyard contributed to this report.