Officer Zach Rolfe, who graduated dux of his police class in the Northern Territory just over three weeks ago, swam across the raging river multiple times to rescue the two tourists.

The former Canberra Grammar student had his first shift with Alice Springs police on December 19; by Tuesday - December 27 - he was performing rescues worthy of a bravery award.

The former army officer who did a tour of Afghanistan was laidback on Thursday talking about his amazing feat, explaining how at one point he literally swam from tree to tree in the flooded river.

"I was confident in the water because of my past training," The 25-year-old said.

"I knew the main danger in the water was freaking out. If I started to freak out, I'd be gone in a second. So every time the current became too strong, I'd just chill out and wait until it carried me to a better place."

The tourists - a woman, from Hong Kong, and a man, from Taiwan - had been driving in a hire car that was swept away in the flood waters west of Alice Springs on Tuesday, local media reported.

The first rescue occurred when the man was found clinging to a tree in the middle of the swollen Hugh River, weak and distressed thinking his partner had been swept away and drowned. She was nowhere to be seen.

Officer Rolfe and Acting Sergeant Kirstina Jamieson and a member of the public, Michael Priestly, took off their shoes and clothes to swim to the man and rescue him with the help of just a rope.

"The water was pretty wild at that point," he said. "It was deep and the current was extremely strong."

The trio was able to get the man to tie the rope around the chest and then inch him back across the water onto a small island in the river.

Officer Rolfe then volunteered to swim to the other side of the river and walk downstream in search of the woman.

"Sarge said she did not want me going into the water unless I was confident I could get to the other side," he said.

"I just got in and swam as hard as I could."

He travelled about 5km downstream in search of the missing woman, all in in his underwear, sometimes in the water, going past sheer rock faces, sometimes on land being scratched by thick vegetation.

"I didn't think there were crocodiles in the water but I wasn't sure because I'm not from the Northern Territory," he said, with a laugh.

Officer Rolfe kept calling out the woman's name until he heard a faint reply, the woman lying on an island where the river forked into two.

"I kind of just jumped in and used the current to push me into the trees where I'd have a rest until I got to her," he said.

"In the middle of the river, I did think, 'This is a dumb decision' but it turned out pretty sweet."

His father, Richard Rolfe, told The Canberra Times, the woman was extremely distressed, thinking her partner had drowned.

"Zach was able to calm her down and explain to her that her husband was alive," Mr Rolfe said.

"She said to him they'd now have to wait for the police and Zach, in his pink underpants, had to explain that he was the police."

Well, the undies were black with a pink trim, Officer Rolfe confirmed.

"They're Tradie's, good undies," he said.

Officer Rolfe said the woman was extremely weak so he carried her across the river. "She just clung to my neck," he said. The pair then walked barefoot back to the other police, taking almost an hour to get to safety.

The woman was taken by helicopter to hospital; her partner by ambulance.

"Everyone was pretty happy to see us," Officer Rolfe said.

What made the rescues even more incredible was that the police were working in isolation, there was no mobile or radio signal and emergency personnel could initially not get through due to another flooded creek.

Officer Rolfe had only praise for his superior, Acting Sergeant Jamieson and the civilian Michael Priestly, deflecting praise from himself and the fact he put his own life at risk.

"I think every cop does that at some point and if I didn't do it, someone else would have," he said.

Mr Rolfe said Zach was his and Debbie's "baby" but they had faith in the capabilities of their super-fit son.

"All I can say as a parent is we are very confident in Zac's ability to do anything and we are completely comfortable with the decision to let Zach take the initiative [in the rescues]," Mr Rolfe said.

"He's a very resourceful young man. We're obviously incredibly proud of him."

Acting Superintendent Brendan Muldoon, from Northern Territory police, said the actions of the police officers were "very courageous" and they had undoubtedly put themselves in harm's way to rescue the tourists.

"[They did so] on the pure belief if they didn't go in, then someone would have died," he said.

Mr Rolfe, a well-known Canberra car dealer, and Mrs Rolfe, a partner in a local law firm, are renowned for their charity work in the national capital, and were ACT finalists in the local hero category of the Australian of the Year awards in 2014.

The Rolfe clan was otherwise busying celebrating patriarch Owen - Richard's father's - 82nd birthday on Thursday. Officer Rolfe had spoken to his grandfather, who wasn't about to let him get a big head.

"He told me he wants 10 witnesses before he'll believe it," Officer Rolfe said, with a laugh.