An Alexandra man has become a rescuer for the second time, after he and a childhood friend leapt into Lake Dunstan to save a man whose ute had taken an icy plunge.

Police publicly praised their heroic actions, as the driver of the ute - who is in his 60s - was taken to Dunstan Hospital in a serious condition.

Alexandra resident Regan Healey, 42, was driving home on State Highway 8 on Thursday when he saw the erratic oncoming ute about 5.15pm.

"He was coming towards me and was wobbling all over the road within his lane," Healey said.

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"As he passed me I looked in the rear vision mirror to see him go off the bank."

Healey spun his car around and headed back to help.

Fortunately, the truck had stayed on four wheels, he said.

It was by pure chance that his high school mate Benji Saunders was travelling in the car behind him.

Saunders was already helping the driver out of the ute when Healey arrived.

"He [the driver] wasn't getting himself out," Healey said.

The car was about 20 metres into the lake, and submerged up to the bonnet, Healey said.

"He was conscious when we got him to the bank and then he deteriorated very quickly.

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"We took care of him until the ambulance arrived."

Healey was well versed in first aid from his work as a lineman, and from five years in the Alexandra Fire Brigade.

Yesterday, Constable Leon Burdett said the public did a wonderful job helping the man escape before emergency services arrived.

"I'd just really like to thank the group who rushed to the man's aid and got him out of the lake, we're really grateful," he said.

The ute has been removed from Lake Dunstan and an investigation into the cause of the crash is under way.

Healey's quick thinking first made headlines in 2016 when he saved the life of a choking 9-year-old.

Healey had been in Auckland to attend the New Zealand Tattoo and Art Festival.

He was eating at a restaurant in Burswood when he noticed a mother panicking and the wee boy about to pass out.

Before he knew it he was right in the middle of it.

Healey had told the Otago Daily Times the young boy could not breathe so he used the Heimlich manoeuvre to clear his throat.

"I got that out - along with everything else he'd been eating."

Today, Healey told the Herald he was still in touch with the boy's family.

The condition of the ute driver was not known.