The possibility of drugs as a factor is also being investigated, Maui police Lt. Wayne Ibarra said.
A 21-year-old man was driving a 1998 Dodge Neon north on Kula Highway in the island's Upcountry area about 6:30 a.m. Sunday when he lost control, spun into oncoming traffic and collided with a 2003 Suzuki Aerio carrying three people, Maui police said.
The impact of the collision tore the Neon in half, sending the two halves about 185 feet apart. All five passengers were ejected and killed.
Police said only the driver was wearing a seat belt. He was taken to Maui Memorial Medical Center with serious injuries. His identity was not released.
Those killed were identified as Remington Taylor Redwell, 20, of Lahaina, Steven Shaw, 20, of Lahaina, Annastachia Cruz-Kalua, 19, of Pukalani, Ambrose Momoa, 20, of Waiehu, and Karl Barrack, 20, of Pukalani.
Two were culinary students at the University of Hawaii's Maui College, KHON-TV reported.
Barrack was taken to Maui Memorial, where he died. The others died at the scene, police said.
The driver of the Suzuki, a 46-year-old Pukalani man, and the front-seat passenger, a 47-year-old Pukalani woman, were taken to the hospital, where they were treated and released. Both were wearing seatbelts.
A 55-year-old Pukalani woman sitting in the backseat and not wearing a seatbelt was hospitalized in stable condition.
Ten people have died in traffic crashes in Maui County this year, compared with three at the same time last year.
The crash on Sunday was one of Maui's deadliest.
Police closed Kula Highway for about six hours after the crash. Police warned motorists to drive with safely over the long weekend, especially with Monday being a state holiday.