A powerful explosion killed at least two people and injured 19 others Thursday when a small plane crashed into a furniture factory in Southern California shortly after takeoff from a nearby airport.

The four-seat plane crashed into the sprawling building on Raymer Avenue near Fullerton Municipal Airport in Orange County just after 2 p.m., about 25 miles southeast of Los Angeles, authorities said.

Benjamin Torrez, who helps load furniture onto trucks, was nearing the end of his shift when he and his colleagues heard a loud collision followed by screams. Mr. Torrez, 57, ran outside to see a horrific scene: A crashed plane burst into flames as some of his colleagues frantically used fire extinguishers on three or four workers who had caught fire.

“We know almost everyone, but we don’t know them well,” Mr. Torrez said of the workers, who he said worked in other parts of the camp.

“Many were burned,” he added. “I was afraid.”

Officials estimated that up to 300 people were evacuated from the building, which suffered extensive damage from the crash and fire. Nineteen people were treated for their injuries, including some who were taken to the hospital, said Mike Meacham, deputy chief of the Fullerton Fire Department.

The two people killed have not yet been identified and it is not clear whether they were aboard the plane, officials said.

According to Eliott Simpson, an investigator for the National Transportation Safety Board, the plane had climbed to an altitude of 900 feet before the pilot requested an immediate return to the airport.

The pilot then made a 180-degree left turn to return but crashed into the building about 1,000 feet short of the runway. He did not signal what might be wrong with the plane before the crash, Mr. Simpson said at a news conference Thursday evening.

Surveillance footage captured by a local television station from a nearby building showed the moment of impact as the plane exploded in a huge fireball as it hit the roof of the facility. Separate aerial footage on local television showed smoke rising from a large hole in the roof.

The plane was a Van’s RV-10, a popular kit airplane that owners can build and maintain themselves, Mr. Simpson said. The plane that crashed Thursday was built in 2011 and the owner was listed as a resident of Huntington Beach, California. He could not immediately be reached for comment.

Officials said it was unclear where the plane might have been headed, adding that weather most likely did not play a role in the crash. Mr. Simpson said the NTSB would continue its investigation on Friday and recover the plane by Friday evening.

Over the years, there have been several accidents involving small aircraft flying in and out of Fullerton Municipal Airport.

In November, two people were injured when a plane taking off from the airport had to make an emergency landing and crashed into a tree just a street from the scene of Thursday’s accident. In 1995, the airport came under intense scrutiny after a plane attempting to land there crashed into a townhouse complex, killing two people on board and a third person inside.

Jack Begg contributed to the research.