McCLELLANVILLE — Federal investigators are combing through the wreckage of a small plane that crashed Thursday afternoon in a swampy area north of Charleston, trying to find out why the plane went down, killing two people on board.

Investigators with the Charleston County Coroner’s Office were on scene after dark and did not immediately release the identities of the two people who were killed.

Witnesses said a small plane was seen spiraling toward the ground just south of McClellanville around 5 p.m. Calls to 911 dispatchers sparked a massive search for the wreckage. The plane was found a couple of miles past the end of South Tibwin Road, in a former rice field near the Intracoastal Waterway.

It’s a swampy area full of alligators, snakes and mosquitoes. Searchers had to build temporary bridges between patches of high ground to get in with their all-terrain vehicles.

The plane apparently barreled through the woods for 140 feet. The damage path was 10 feet wide.

Deputies and rescuers reported smelling fuel at the site, but no hazardous material was spilled, Awendaw Fire Department Battalion Chief Fred Tetor said later.

The Federal Aviation Authority identified the plane as a Rockwell International 690B, an 11-seater with two engines.

The plane left the Johns Island Executive Airport at 4:30 p.m. on what was supposed to be a 53-minute flight to Georgetown and back.

Officials at the airport said two people were on board, including a person in flight training.

The last listed owner of the plane, dated in September 2011, was Nighthawk Air LLC of Matthews, N.C.

Motorists on U.S. Highway 17 called 911 to report seeing a plane going down near the Intracoastal Waterway.

Residents heard the crash.

Ruthie Merritt, who lives on Lofton Road, said she heard what sounded like a propeller plane in the air, then a loud noise.

“It was just one big boom,” Merritt said.

Dave Munday, Natalie Caula, Andrew Knapp, Schuyler Kropf, and Glenn Smith contributed to this report.