The Tauranga police officer who is being hailed a hero for a saving the life of a crash victim this week has described his instinct-driven decision to dive from a bridge into cold waters.

Constable Deane O'Connor's actions after a van was shunted off Tauranga's Maungatapu Bridge on Monday night are thought to have saved the life of a passenger who managed to free himself from the van.

In a statement released this afternoon, Mr O'Connor said one of the difficult parts of rescuing the 23-year-old from the water - an exhausting struggle that took 30 minutes - was that he knew his friend in the driver's seat, 24-year-old Gregory Woledge, was gone.

"It's very hard because you feel elated that someone has survived, but you also can't help feeling for the family who have lost someone, especially someone who is a young dad," said Mr O'Connor, who has been rostered off since the tragedy.

"I've got four kids and I'd be devastated. My heart goes out to his family."

One of the most common questions since Monday has been around his thought process that night and what makes someone make the decision to put their life on the line.

He was first on the scene, arriving just a minute or two after the call went out on the radio.As he got out of the car, people were telling him that someone was in the water, going under and screaming for help. Dean immediately took his police safety vest off.

"I hadn't even made a decision at that point; hadn't thought about jumping in. For some reason I just took the vest off and threw it in the back of the car," he said.

"I went to the bridge, someone had a torch on him and I saw him go under the water and then come back up again. I just started stripping down. I could hear someone saying 'someone has to do something'; and some people saying 'you can't go in, you won't make it' and I kind of just ignored that. It was a calculated risk - I assessed the situation pretty quickly.

"I don't think I ever thought I couldn't do; it's hard to explain. I've never felt fear like it. I was shaking and am not sure whether that was the cold or the anticipation of what I was about to do.

"It was only when I climbed over the rail that I actually started thinking 'what am I doing?' and then I saw him go under again and for that split second everything went calm and I just jumped."

Mr O'Connor, who wouldn't call himself a strong swimmer, credited his own survival in part to the unnamed passenger.

The pair talked the whole time they were in the water.

"It was just about keeping each other happy and keeping going. We just talked about all sorts; I can't remember what.

"My focus was just on keeping him calm. I knew I could last as long as my body would let me; I wasn't tired at all. He pretty much helped me get out in a sense. It's quite scary; you're really fighting that urge to panic and all my talking to him was actually helping to keep me calm."

Mr O'Connor has also been overwhelmed by the response to his actions

Numerous messages of support and best wishes have been sent to him via Tauranga Police Station and social media.

"It's quite humbling. I don't like being in the limelight; I struggle with this kind of thing and if I could hide under a blanket I would."