Two police officers and a civilian who stripped down to their underwear to help rescue a man clinging to a tree in a flooded river have had their actions recognised with a national bravery medals.

Senior Constable Kirstina Jamieson and Constable Zachary Rolfe were called out to the Hugh River, 30 kilometres from Alice Springs, in December 2016, during widespread flooding.

Two tourists were missing after their car was swept away when they attempted to cross a flooded road.

"They were driving their vehicle down the flooded causeway and it got swept away with them in it," Senior Constable Jamieson said.

"When I got to the river I could see that it was really very wide and very rapid, so I just had to get a plan together to try to save these people."

They saw a man up a tree in the middle of the "raging" river, the water so high it was lapping at his feet.

The man was a tourist from Taiwan who spoke no English, couldn't swim, and was frightened of water.

Acting Sergeant Kirstina Jamieson at the Alice Springs flood rescue site. ( ABC News: Grenville Turner )

The two officers enlisted the help of another man, Michael Priestley, to help.

"Me and two other that were reasonable swimmers found a rope and we swam out and managed to save this person," Senior Constable Jamieson said.

While there was a risk to the small team, they tried to take measures to minimise the danger, she said.

With no life jackets, the trio, carrying a rope, made their way across the river to a land bank near the stranded man, throwing him a rope to tie around himself and the tree.

They got him to take his jeans and shoes off, and Mr Priestly swam across floodwaters to the opposite riverbank to attach the rope at the other side, where a waiting officer and paramedic pulled them back to safety.

Acting Sergeant Kirstina Jamieson (L) and Sergeant Zachary Rolfe (centre) helped rescue two tourists. ( ABC News: Grenville Turner )

Second rescue after five-kilometre trek in underpants

With the man's travel companion still missing, Constable Rolfe swam back out across the torrent and walked for five kilometres down along the bank to search for her.

It was only his first week working for the Northern Territory Police.

"He swam across the rest of the river to the bank that no one else could get to, and he walked about five kilometres probably down that river bank to search for the woman, dressed only in his underpants," Senior Constable Jamieson said at the time.

He found the woman in the middle of a fork in the river, with an injured hand from trying to smash out the car window so she could escape.

"[He] then had to swim again across the raging river and walk her back her to safety," Senior Constable Jamieson said.

The pair then had to walk back barefoot for kilometres.

Police officer Zachary Rolfe played a pivotal role in rescuing tourists from flood waters. ( ABC News: Grenville Turner )

Now both officers have been awarded a national police bravery medal for their actions.

"I'm very proud to have such an award given to me and the people who helped me on that day, I'm pretty excited about it," Senior Constable Jamieson said.

"This rescue wasn't a one-man rescue, it needed a team, and we had a really good team involved. The whole rescue couldn't have been done without everyone involved."

Senior Constable Jamieson said she would be celebrating her achievement with "a few drinks, probably".