State and federal officials will deploy hundreds of more people to help respond to the oil spill off the coast of Orange County, Calif., Gov. Gavin Newsom said Tuesday.

Mr. Newsom, who attended a briefing with state, federal and local officials in Huntington Beach, said at a press conference that there will be about 1,500 people on site to help with cleanup efforts by Wednesday, up from about 300 Tuesday. Multiple agencies are working to contain the damage created by a leak connected to an offshore oil platform over the weekend.

Earlier in the day, federal officials identified a 13-inch split in a sea bottom pipeline as the likely source of the oil spill, but said they aren’t yet sure if it was caused by an anchor dropped in the wrong location.

The tear was discovered by commercial divers who found 4,000 feet of the 17.7-mile pipeline from an oil-processing platform was displaced as much as 105 feet, Coast Guard Capt. Rebecca Ore said in a press briefing.

Capt. Ore, sector commander for the Los Angeles-Long Beach region, said there had been no confirmation that a vessel had been anchored above the pipeline, but said an investigation remains under way.

She said divers reported no more oil was coming out from the rupture, where up to 130,000 gallons was discovered spilled Saturday. Crews as of Tuesday had recovered nearly 5,000 gallons of the crude, while biologists tended to eight birds that have been found coated in oil. Cleanup workers were deployed in coastal Orange County cities from Huntington Beach to San Clemente, about 35 miles south, to intercept crude washing up.

In the briefing, Capt. Ore provided new details on the timeline of when the spill was first discovered. She said a “good Samaritan” on Friday evening reported to the federal National Response Center that a sheen of unknown source was floating in the waters off the coast of Huntington Beach. Coast Guard officials followed up with a call to the reporting party but couldn’t get information specific enough to follow up on.

In the predawn hours Saturday, a second report came in from the National Oceanic and Atmospheric Administration that its satellite imagery showed “a possible oil footprint,” Capt. Ore said. The spill was discovered later Saturday morning, and that is when Amplify confirmed it, federal officials said.

Asked why they didn’t respond Friday night, Capt. Ore said the Coast Guard was following procedure, and that spills can be difficult to detect at night. Reports of possible leaks and spills in the area are common, she added, and often don’t pan out.