Two civilian contract workers were killed and two others injured Wednesday while working on a barge at Pearl Harbor’s Naval Inactive Ship Maintenance Facility off Waipio Peninsula.

The four civilians were working on a floating concrete block when a 10,000-pound buoy fell about 70 feet, partially hitting two of them. The two others were injured while getting out of the way to avoid being hit.

The workers were all employed with Healy Tibbitts Builders Inc., which specializes in marine construction.

"We are devastated to learn of the loss of two members of the Healy Tibbitts family," Rick Heltzel, company president, said in a statement. "Our thoughts and prayers are with the families at this extremely difficult time. We do not yet know what caused the incident and will be working with the Navy and other agencies to investigate this tragic event."

The Navy also issued a statement expressing condolences to the families and friends of the victims. "A full investigation into the incident is under way, and we will work closely with local officials and agencies," Navy officials said.

The workers were strengthening mooring lines on the 820-foot decommissioned amphibious ship Tarawa, which uses a number of the circular white buoys, an official said. The Navy said the incident occurred during the replacement of the buoy.

The industrial accident on a barge with a crane was reported at 10:19 a.m.

One of the civilian contractors who died was a man in his 40s and the other was in his 30s. A 50-year-old man and a 27-year-old man were reported in stable condition following the accident.

Honolulu Fire Department spokesman Capt. David Jenkins said the men were onboard a barge that was servicing the Navy’s fleet of inactive ships.

Two of the men were knocked or jumped into the water to avoid the buoy, which was 12- to 15-feet in diameter. One man reported jumping 15 feet from the concrete barge into the water.

Jenkins said firefighters received a 911 call at 10:19 a.m. and arrived at the scene six minutes later. The contractors were still on the barge, so firefighters didn’t reach them until 10:39 a.m.

James Ono, 26, a laborer working for a subcontractor, said he was working on another crane when the accident happened.

"We sent out a Lifeline (stretcher), but EMS (Emergency Medical Services) arrived" before getting it to them, he said.

Another worker said he knew the man who died but didn’t know his name.

The facility is owned by the Navy as a holding area for decommissioned naval vessels pending determination of their final fate, and is part of the Naval Sea Systems Command’s Inactive Ships Management Office based in Portsmouth, Va.

Naval Sea Systems had 13 ships in the Pearl Harbor’s Middle Loch in 2013.

The area is located off Waipio Point Access Road, past Waipahu High School, near the Ted Makalena Golf Course and the Waipio Peninsula Soccer Complex.

Star-Advertiser staff writer Leila Fujimori contributed to this report.