Six people were injured after a head-on collision in the Lindis Pass, near Cromwell, on Sunday.

Five people remain in a serious condition in hospital after a crash in the Lindis Pass in Central Otago.

Senior Sergeant Darryl Lennane said police were still investigating the crash which occurred about 4.50pm on Sunday.

The crash involved several vehicles, he said.

"A 36-year-old man from one vehicle and a 35-year-old man and three women aged 27, 30, and 31 years of age from the second vehicle, have all been hospitalised with serious injuries as a result of the crash."

Details of the cause of the crash would be made public once the investigation was complete, he said.

A car-load of off-duty doctors were the first to arrive at the scene of a head-on collision in the Lindis Pass, near Cromwell.

Police, ambulance and the Fire Service attended the scene of a two-car crash on the south side of the pass in the South Island's Mackenzie Basin.

Fire Service communications shift manager Andrew Norris said they were alerted to the "head-on collision" at 4.45pm on Sunday.

Norris said there were six patients. Three people were in a serious condition and three had received moderate injuries.

One person had to be cut from one of the vehicles.

"We were fortunate that some of the passing motorists were doctors. Luckily, there were a couple of doctors on the scene long before any of the emergency services arrived."

He understood there were up to four doctors who had helped at the scene.

St John arranged the response from rescue helicopters, including one from Queenstown, and a further two had arrived from Dunedin.

St John communications advisor Robbie Walker said one female patient had been transported to Dunedin Hospital via helicopter, in a serious condition.

Another patient, who was also in a serious condition, had been taken to Dunedin Hospital in a rescue helicopter.

An ambulance had taken two people, both with moderate injuries to Dunstan Hospital and two patients, with serious and moderate injuries, had remained at the scene.

In a statement, police urged motorists to be patient to allow the services to deal with the crash.

It was raining in the area, with poor road conditions. The road was blocked and would cause traffic to back up and be delayed.

There was no immediate detour available for traffic.

The NZ Transport Agency advised motorists to avoid the area or follow the directions of emergency services at the scene.