A single-engine, Piper PA28 airplane crashed underneath a Moanalua Freeway bridge in Mapunapuna early Friday afternoon, seriously injuring the three men on board.

Shayne Enright, spokeswoman for the city Emergency Medical Services, said the three men, in their 20s, were all taken to a trauma center in serious condition but suffered no major injuries.

Federal Aviation Administration spokesman Allen Kenitzer said the plane “crashed under unknown circumstances.”

All lanes of the Moanalua Freeway, above the crash site, remained open.

The plane was manufactured in 1971 and registered to Jahn P. Mueller of Honolulu, according to FAA records.

Monique Bardo, director of operations for Ballard Mortuaries, was outside when she saw the plane flying above the canal then suddenly crash and explode underneath a bridge that crosses the water.

“The pilot got everybody out,” Bardo said. “It was right in the canal when it crashed. It was really loud. There was lots of black smoke that went all over the (Moanalua) freeway.

The mortuary, which is separated by a chain link fence from the crash site, was full of employees and mourners, she said.

“My gosh, it was so spooky,” Bardo said.

Honolulu firefighters received a report of a downed plane around 1:25 p.m., said Fire Capt. David Jenkins.

Kenitzer said the FAA and National Transportation Safety Board will investigate.