Two people have died in a fiery outback crash in South Australia that has collapsed the surface of the Stuart Highway.

The driver of a ute — a 23-year-old man from the ACT — and the passenger of a B-double truck — a 57-year-old woman from the Adelaide suburbs of Para Vista — died when their vehicles collided about midday yesterday on the Stuart Highway at Wirraminna, in the state's far north, between Pimba and Glendambo.

Both vehicles caught fire on impact.

The truck driver — a 49-year-old man from Para Vista — is in a critical condition in hospital.

The road surface of a floodway and its surrounds collapsed under the intense heat from the fire.

Police say the highway will stay closed to all traffic for several days.

Judy Tut, who was on her way back home to Alice Springs from Victoria, said police at the scene told her it could even be longer.

"They said it could take a couple of weeks or actually months," Ms Tut said.

Trucks have been taking to the Oodnadatta Track as an alternative to the Stuart Highway.

Fatal ute rollover near Morgan

In another incident, a man has been killed in a rollover on a private property in the Riverland.

Emergency services were called to a private property off Wonga Road, at Lindley — near Morgan — after reports of a single ute rollover about 6:00pm yesterday.

Police did CPR on a 26-year-old Campbelltown man until paramedics arrived but he could not be saved.

The driver of the ute, a 29-year-old Athelstone man, and two other passengers, a 34-year-old Tanunda man and a 29-year-old Klemzig man, were all flown to Adelaide with non-life threatening injuries.

Motorcycle crash in south-east

In the state's south-east, a 63-year-old male motorcyclist has suffered life-threatening injuries after a crash at Kongorong, near Mount Gambier.

The man came off his bike on an unnamed access road off Bannisters Road about 5:50pm yesterday.

A total of 21 lives have been lost on South Australia's roads this year, compared with 17 at the same time last year.