Authorities have recovered human remains and a wallet following a plane crash Tuesday a mile offshore of the Pier Avenue beach ramp in Oceano, according to the U.S. Coast Guard.

Work at the scene has been suspended for the night, and the effort has switched from rescue to recovery.

Under an unseasonably hot afternoon sun, a team of emergency responders from seven county and state agencies gathered at an impromptu beach command post to search for survivors in response to a report of a downed aircraft in the ocean.

At the scene were officials from the San Luis Obispo County Sheriff’s Office, State Parks, Five Cities Fire Authority, Cal Fire, and the Pismo Beach Police Department.

Vessels from the Port San Luis Harbor Patrol and Coast Guard searched the water as California Highway Patrol helicopters circled overhead.

According to Cal Fire Battalion Chief Eric Shalhoob, the agency received a report from a witness claiming to see a medium-sized aircraft go down at approximately 2:10 p.m. Shalhoob said one witness also reported seeing a splash in the water.

At about 2:40 p.m., officials confirmed seeing debris in the water along with an oil slick, according to the Five Cities Fire Authority. The water is estimated to be about 70 feet deep in that area.

Pismo Beach resident Norm Staswick was on the beach near Pier Avenue when he heard what he said sounded like a plane engine overhead before he heard what he described as an explosion, though he said he did not see any aircraft.

“I definitely heard a loud boom,” Staswick said.

The sheriff’s dive team was notified, as was the U.S. Coast Guard, who began searching beyond the breakers using sonar and personal watercraft.

At approximately 4:30 p.m., Sheriff’sOffice spokesman Tony Cipolla confirmed that a plane had gone down roughly one mile offshore, though he said it was not yet known where the plane departed from, where it was headed, or how many people were on board.

It is believed to have been a single-engine plane, he said.

The weather was working in emergency responders’ favor, with very good visibility and ideal conditions for a search-and-rescue operation. But as the sun began to set, no wreckage had been located, and officials reclassified the operation from a rescue mission to a recovery, which means they did not expect to find any survivors.

It was not specified as to what type of debris was found.

As officials continued their investigation with area airports, it also remained unclear where the aircraft came from.

The Oceano County Airport is not a controlled air space, so there would be no record if a pilot took off or planned to land there, said Craig Piper, assistant general manager for San Luis Obispo County’s airport services.

Pilots are not required to file a flight plan, and the airport doesn’t have an air traffic control tower.

Tuesday’s nice weather made for a busy day at the airport, Piper said, “but there’s no record that, if in fact there was an aircraft that went down, who that might have been.”

The Sheriff’s Department’s search remains ongoing.

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State Parks and Cal Fire officials were among those investigating a downed aircraft near Oceano. (David Middlecamp / San Luis Obispo Tribune photo)