Police initially feared "at least four lives" had been lost after a Ford Ranger allegedly crossed onto the wrong side of the Northern Territory's Stuart Highway and struck a Toyota HiAce on Wednesday.
However police on Thursday confirmed a fifth person had died after working through the night to identify the victims and speaking to their families.
The driver and three occupants of the Ranger died in the crash that occurred about 75km east of Darwin around 12.50pm on Wednesday - two men and two women aged from 23 to 36.
The sole occupant of the Toyota - a 69-year-old woman - also died.
"Both vehicles sustained catastrophic damage and caught fire shortly after impact," a Northern Territory Police statement said.
Good Samaritans had tried to help after the vehicles collided, police said.
"However, the occupants were unable to be extricated before both vehicles became fully engulfed in flames," police said.
Investigators are still trying to piece together what caused the collision but witnesses claimed the Ranger was speeding in the lead-up to the crash, police said.
"This is an incredibly tragic incident that has claimed five lives and will have a devastating impact on multiple families and the wider community," Detective Senior Sergeant Michael Schumacher said.
"Witnesses have told investigators the utility was travelling at excessive speed and overtaking dangerously in the minutes leading up to the collision.Â
"We urge anyone who witnessed the driving of either vehicle prior to the crash, and who has not yet spoken to police, to come forward."
Detours are in place at the crash site on the Stuart Highway which remains a crime scene. Delays are expected in the area.
Anyone with information should contact police.
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