Four people are dead after a civilian-contracted helicopter crashed at a U.S. naval facility, officials said.

       The incident occurred at the Pacific Missile Range Facility, a Navy base in Kauai, Hawaii, shortly after 10 a.m. local time Tuesday.

       The helicopter was taking part in a range training operation on the base in Kekaha when it crashed on the northern area of the installation, a Pacific Missile Range Facility spokesperson said in a statement.

       Pacific Missile Range Facility, FILE

       Marines board a CH-53 helicopter onto Pacific Missile Range Facility in Barking Sands, Hawaii, July 29, 2016.

       Emergency personnel responded to the crash, the spokesperson said. There were four fatalities. The names of those killed have not yet been released.

       The helicopter was operated by Croman Corporation, which "provides range support services" to the base, the Pacific Missile Range Facility spokesperson said. ABC News has reached out to Croman Corporation for comment.

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       An investigation is underway to determine the cause of the accident, the spokesperson said.

       The National Transportation Safety Board also confirmed it is investigating the crash of a Sikorsky S-61N helicopter near Kekaha.

       Pacific Missile Range Facility is the "world's largest instrumented, multi-dimensional testing and training missile range," according to the U.S. Navy. It has over 42,000 square miles of controlled airspace.