Northern Territory Police say it is "really unusual" for three people missing in Central Australia for 10 days to not have contacted family, as an air search for them has been expanded.

Key points: NT Police say the trio's bank accounts and phones have not been accessed

NT Police say the trio's bank accounts and phones have not been accessed Police have expanded the air search area using a plane instead of a helicopter

Police have expanded the air search area using a plane instead of a helicopter Temperatures in the region for the past 10 days have ranged from mid to high 30s with two days above 40 degrees

Alice Springs residents Claire Hockridge, 46, Tamra McBeath-Riley, 52, and South Australian man Phu Tran, 40, were last seen at a unit on Elder Street in Alice Springs on Tuesday, November 19.

NT Police Superintendent Pauline Vicary said no-one in the group had accessed their bank accounts or phones since their departure.

"This is really unusual," she said.

Police believe they left Alice Springs in a late model white Mitsubishi Triton, with South Australian registration plate S483 AAI, after telling friends and family they were going on an "afternoon trek".

The trio was reported missing on November 23 and police began an air search three days later, focused on areas south of the town near Owen Springs, Stuarts Well and Rainbow Valley.

The search has now been expanded to include the region further south, near Finke and Kulgera, with a police plane covering the southern part of the Stuart Highway.

"The information that we have is that they regularly keep contact with their families, they haven't even contacted their families and there's nothing happening with their phones."

Superintendent Vicary said the ute had a black soft cover, a front nudge bar, two round halo lights and a UHF aerial.

South Australian man Phu Tran is among the group of three missing in Central Australia. ( Supplied: NT Police )

She said Ms Hockridge was wearing blue cargo pants and a blue short-sleeved t-shirt with a motif and Mr Tran was wearing tan cargo shorts with a red t-shirt — it is not known what Ms McBeath-Riley was wearing.

"We're asking anybody who's going to be travelling back to stations or communities around Titjikala, Santa Teresa, Finke, Kulgera if they can keep an eye out and if they do see the vehicle to let us know," Superintendent Vicary said.

"We cannot emphasise how concerned we are, if anybody is travelling on those backtracks, please keep your eye out."

Police concerned about 'limited supplies'

Police believe the group was travelling with a blue Staffordshire terrier with white markings, which is named 'Raya' according to a social media post from Ms Hockridge's family.

Superintendent Vicary said it was not known what supplies the group had with them but police did not believe they had bought new supplies from any nearby roadhouses.

"We have to go on the basis that they had limited supply," she said.

"We are very concerned that if they did have supplies that they would have run out by now."

Temperatures in the region have ranged from the mid to high 30s, with two days above 40 degrees.

Superintendent Vicary said there was no point conducting ground searches until the ute was found because the current search area was too large.

She said there had been some initial discrepancies in the information provided to police.

"A lot of the information that we're getting isn't coming directly from people that have spoken with them," she said.

"Information that has come through the family initially was third hand, so obviously things can get lost in that translation.

"We'd rather that people just confine their comments on social media to supporting the family, who are obviously extremely distressed at this stage."