Investigations are continuing into the cause of a car crash which killed five people about 100 kilometres south of Darwin on Friday.

Northern Territory Police say the two cars travelling in opposite directions north of Adelaide River smashed into each other on the Stuart Highway about 4:00pm.

Five people from a sedan were killed and the driver of a four-wheel drive was taken to hospital in Darwin in a stable condition.

Sergeant Mark Casey says police are waiting to speak to the injured driver.

"We'll be speaking to him as soon as we've collected the evidence from this location and we are prepared to speak to him and providing he's well enough to speak with us," he said.

"The speed limit is 110 kilometres per hour which is quite quick when two vehicles do come together, but no there's no indications of speed, alcohol at this stage."

Following the smash at least a kilometre of traffic had backed up along the highway.

During the night, police began to slowly let through small convoys of vehicles.

The Northern Territory road toll now stands at 18, compared with 10 at the same time last year.