Investigators yesterday were still trying to determine why a 22-foot fishing boat exploded early Saturday at the Wai'anae Boat Harbor, injuring six people and hospitalizing four of them — two seriously.

Deborah Ward, spokeswoman for the state Department of Land and Natural Resources, which is overseeing the investigation, said one reason the cause remains undetermined is because investigators are still waiting to interview everyone involved.

"Some of them have been in the hospital," said Ward. "So, they've got to be taken care of first, and then we can go talk to them."

The 6:30 a.m. blast rattled the harbor, threw three fishermen aboard the Nikki B fishing vessel into the air, knocked others nearby off their feet, and hurled debris in all directions.

One of the fishermen, who landed on the pier and seriously injured his back, required surgery at The Queen's Medical Center. Another man, who landed on the boat, was taken to Queen's with a badly broken leg.

Both men remained hospitalized yesterday.

Calvin Nunies, a relative and business partner of Nikki B owner, Dencio Biliboa, 35, said Biliboa was doing better yesterday, but might be paralyzed following his operation.

"We're still just waiting to see what the doctor says," he said.

Nunies said Romeo Gayacan, 52, who landed on the boat, will require reconstructive surgery to correct his leg injuries.

Nunies said he suspected that the explosion might have been caused by a gas leak.

Wai'anae Harbor Master William Aila said Saturday's explosion could be similar to other boat explosions in which a gas leak causes a build-up of fumes that are ignited by some electrical spark.

Boat explosions are one of the leading causes of marine property damage. According to Coast Guard statistics, each year boating explosions and fires injure hundreds of people and cause millions of dollars in property damage nationwide.

Reach Will Hoover at whoover@honoluluadvertiser.com.