UPDATE: 5 p.m.

Chris Turner, owner and captain of Na Pali Riders, a company that offers Zodiac raft tours along the Na Pali Coast, witnessed the crash.

Turner said the helicopter flew over him and his patrons on their way back to Kikiaola Harbor as the aircraft was heading to the landing area by the airport.

“They practically went right over us as they came into the airstrip there before they crashed,” said Turner noting they were less than a third of a mile from the crash site.

The captain said the aircraft appeared normal at the time and that he didn’t hear any unusual sounds coming from the helicopter. The weather was also clear.

Turner saw the helicopter was at the north end of the runway and lowering items when at about 1,000 feet above the strip, the helicopter “erratically” made a sharp turn to the right and went nose down at an accelerated rate.

It swerved, went straight down, nose down right into the runway, Turner said.

The deadly crash happened in a matter of 10 seconds from the time the helicopter flew over the Zodiac to the point of impact.

Turner believes the pilot may have suffered from spatial disorientation at the time of the crash.

He added the helicopter didn’t appear to lose power. “It just went down. It was full speed. It was crazy.”

“Something must’ve malfunctioned for him to not know which way was up or down,” Turner said.

“I was pretty shook,” said Turner who extended his condolences to the family members of the crash victims. “It shook everybody on the boat. It was quiet on the way back.”

Kauai Mayor Derek S.K. Kawakami issued a statement on the crash.

“First and foremost, our thoughts and prayers are with the families and friends of those who were lost this morning in this heartbreaking tragedy,” Kawakami said. “I know there are no words that can express the extent of what you are going through or provide the solace that you need, but please know that our entire community is here for you. We offer our partners at PMRF any resources they may need, and we offer the families involved our deepest condolences during this difficult time.”

UPDATE: 3:35 p.m.

Pacific Missile Range Facility officials confirmed this afternoon that four people died in a helicopter crash on the installation’s north side this morning.

The victims’ identities are not available at this time, they said.

The helicopter was operated by contractor Croman Corp., which was supporting a training operation. Croman provides a range of support services to PMRF, officials said.

PREVIOUS COVERAGE

Military and Kauai County crews are responding to the crash of a civilian contractor’s helicopter on the north side of the Navy’s Pacific Missile Range Facility.

A Pacific Missile Range Facility spokesman said the aircraft crashed on the north side of the installation shortly after 10 a.m. today.

The National Transportation Safety Board said in a tweet that the agency is investigating the crash of the Sikorsky S-61N helicopter.

“More information will be made available, but at this time moment the primary focus is to allow first responders to handle the situation,” said Pacific Missile Range Facility spokesman Thomas Clements in a statement today.

Information on casualties will be released when available, PMRF said in a news release.

The helicopter was flying in support of a training operation, officials said.

A Kauai County spokesperson said county police and firefighters responded and were assisting the military.

An investigation will be conducted to determine the cause of the accident, the release said.

A Kauai County spokesperson said county police and firefighters responded and were assisting the military.

Kauai police were helping the Navy with perimeter security and investigation support, said Coco Zickos, a county spokesperson.

The Sikorsky S-61N is among helicopters built between 1959 and 1980 by Sikorsky Aircraft, which is now part of Lockheed Martin. It was designed to carry a substantial freight or passenger payload.

The helicopters were optimized for use over water, for example, to support oil rig operations. Versions were also used by all branches of the U.S. military. Licensees in the United Kingdom and other countries have also built the aircraft.

This story is developing and will be updated as soon as more information becomes available.

The Associated Press contributed to this report.