Police officers stripped to their underpants and swam across a raging river swollen by floodwaters to rescue two tourists left stranded after their car was swept off a causeway near Alice Springs.

Acting Sergeant Kirstina Jamieson and Officer Zachary Rolfe arrived at the Hugh River, about 30 kilometres west of Alice Springs, at about 1:00pm on Tuesday and saw a man clinging to a tree not far from where his hired four-wheel-drive had sunk.

"The river at this point was approximately 150 to 200 metres wide, it was raging quite a bit," Acting Sergeant Jamieson said.

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

"It was a very short tree … his feet were in the water, he was very, very cold — you could see that — he was very weak at that time."

The two police officers and Michael Priestley, a member of the public who was at the scene, took off their clothes and shoes in order to swim to the man.

"We weren't going to go in with our clothes on, our shoes on … otherwise we would have drowned," 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.

"And from that land bank we managed to throw the rope to the male that was on the tree. He tied the rope around himself and the other part to the tree," she said.

The tourist, from Taiwan, could not speak English and also had to take his jeans and shoes off, she said.

"He couldn't swim, he was very scared of the water," she said.

"[Mr Priestley] swam back over [to the other river bank] with the rope so we could attach the rope to the tree on the other side and he swam back again to assist me and the man," she said.

"And we got on either side of this man and tied the rope around him so that he didn't go anywhere … at this point the river was raging a lot and it was over our heads."

She said another police officer and a paramedic on the opposite bank managed to pull them back in to safety.

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

'We had to get the job done'

Officer Rolfe then swam to the other bank on the Hermannsburg side of the flooded Hugh River and started walking south to try to find the lost woman, who is from Hong Kong, Acting Sergeant Jamieson said.

"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," she said.

He found the woman in the middle of a fork in the river.

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

It is unclear how Officer Rolfe and the woman made it back to the Alice Springs side of the flooded river.

The tourists were cold and in shock after their rescue and were taken to Alice Springs Hospital.

Police said the woman injured her hand trying to smash out the car window, and is undergoing surgery.

The couple are in Australia on a working holiday, police said.

They live in Katherine but were visiting Alice Springs over the holidays, police said.

Sergeant Jamieson said she, Officer Rolfe and Mr Priestley were all confident swimmers.

"Through the whole process we basically evaluated the risks," she said.

"We realised we were the only ones at this point who were able to save this man and we had to get the job done."