The first day of a trial of open speeds on a section of the NT's Stuart Highway has already attracted motoring enthusiasts in high-powered cars.

There will be no speed limits on a 200 kilometre stretch of highway between Alice Springs and Barrow Creek for the next 12 months.

Today a number of high-performance vehicles, including an Aston Martin and Ferrari, have been seen on the road which police are monitoring for dangerous driving.

The Country Liberal Government has come under fire from the NT Opposition, the Police Association and the Automobile Association, for instigating the trial.

Peak medical bodies are also lobbying for the trial to be scrapped.

Doctor Christine Connors from the Royal Australasian College of Physicians NT says the Government is ignoring the evidence.

"Increasing speed increases the risk of a crash, increases the risk of severe injury, increases the risk of someone dying," she said.

"We are going to have people not driving to their capabilities, driving far too fast, and causing unnecessary accidents that might kill themselves or somebody else.

"The evidence tells us that speed kills ... the risk of people dying is very high."

The Police Association has described the trial as purely a political move.

But the Government has defended the decision, saying the onus is being put back on Territorians to drive responsibly.

"The stretch of highway has undergone a multi-million dollar upgrade to improve safety during the trial," Transport Minister Peter Styles said.

"I have heard rumours that there are people from interstate who are coming up here and want to treat it as a street race.

"Sadly for those people, if they do and they do not drive responsibly, then they will probably find themselves being summonsed or arrested by the police."

The Government commissioned four reports on the topic before announcing that open speed limits were back, but the reports have not been made public.