The entire Manhattan Beach coastline was closed to the public Wednesday afternoon after globs of a petroleum-based substance washed up onto the beach.

The material began appearing along the intertidal zone, where the beach meets the ocean, at about 12:30 p.m., said U.S. Coast Guard spokesman Michael Anderson.

“As of right now, we don’t see a source,” Anderson said. “It’s scattered up and down the coast.”

Coast Guard and California Department of Fish and Wildlife officials tested the material but do not expect results for at least a day. The material was being sent to the Coast Guard lab in Connecticut, Anderson said at an evening news conference.

The entire 2-mile stretch of Manhattan Beach coast will be closed until further notice while the site is investigated and cleaned. Lights were turned on for cleanup to continue through the night; about 30 workers in hazmat suits cleaned and collected samples along the shore.

The Coast Guard contracted with Ocean Blue Environmental Services, Inc. to clean the material, which didn’t noticeably harm any wildlife Wednesday afternoon, said Los Angeles County Fire Department’s Lifeguard Capt. Erik Albertson.

“Around (1 p.m.) we noticed a substance coming up on the shoreline that’s in different densities. We’ve closed the beach from the El Segundo jetty to Neptune Avenue,” Albertson said. “It drifted in and seems to have slowed down, but I don’t know.”

It is not clear whether the oil migrated down from the oil spill that occurred May 19 north of Santa Barbara near Refugio State Beach. That spill dumped more than 100,000 gallons of oil from a ruptured underwater pipeline and caused the death of pelicans, dolphins, sea lions and many other species of marine life.

Anderson said nothing is being ruled out as a cause, including leakage from the oil vessels offshore. A Coast Guard helicopter did not find any evidence of an extensive ocean spill when it searched the Manhattan Beach area Wednesday.

“They didn’t see any sheen on the water or product of concern,” Anderson said. “At this point, they haven’t been able to determine what it is.”

Manhattan Beach Mayor Wayne Powell, who was at the L.A. County Lifeguard Headquarters, said the oil washing ashore does not appear to be coming from a natural source.

“We do have natural seepage, but not in the quantities we’re experiencing,” the mayor said.

Several onlookers and dozens of personnel from local fire departments were at the scene Wednesday night. A long-time resident of Manhattan Beach, Leanne Meyers, said “the water looks beautiful,” noting one would have to be up close to notice the oil and tar.

The same substances also surfaced on two miles of beach in Oxnard on Wednesday, prompting similar concerns that it was connected to the Santa Barbara County oil spill, KABC Channel 7 reported. Environmental experts, however, said the oil and tar was in fact a natural occurrence and the beach was safe, according to the news agency.

The Los Angeles County Department of Public Health posted closure signs along Manhattan Beach, and residents are advised to avoid contact with the ocean or wet sand and any materials that wash ashore.

Recorded information on beach conditions is available 24-hours a day on the county’s beach advisory hotline at 800-525-5662. Information is also available online at http://www.publichealth.lacounty.gov/beach.

Staff writer Donna Littlejohn contributed to this report.