The crash occurred around 9:30 p.m. local time Wednesday about a mile from Lanai Airport in the Miki Basin area, Maui County spokesman Rod Antone told The Associated Press.
The plane, a twin-engine Piper PA31, burned upon impact, according to Federal Aviation Administration spokesman Ian Gregor. He was unable to provide a tail number.
Three people were killed and three were injured, Antone said.
Authorities said that they believe everyone aboard the aircraft has been accounted for.
Maui County identified the dead as the pilot of the plane and two Department of Planning employees. Two other planning employees were in critical condition and the deputy attorney for Corporation Counsel was in serious condition Thursday morning, according to a nursing supervisor at Queens Medical Center and the county. All three survivors were airlifted to the hospital. No names were released.
The group had been on Lanai earlier that evening to staff a Lanai Planning Commission Meeting and chartered a return flight on Maui Air, KITV reported.
Fire Services Chief Lee Mainaga said crews located the aircraft in grasslands about a mile southwest of the airport. Firefighters quickly doused a small brushfire ignited in the crash.
The National Transportation Safety Board would lead the investigation into the cause, with assistance from the FAA, Gregor said.
Billionaire Larry Ellison, the CEO of Oracle Corp., bought 98 percent of Lanai in 2012. He later told financial news channel CNBC he envisions Lanai becoming a "little laboratory" for experimenting with more environmentally sound ways to live.