Additional police units were at the Ōkahu Bay boat ramp within minutes, with a police boat also arriving in the bay.
Members of the public came to lend a hand from pontoons.
Graham said the vehicle became submerged and police had to extract the man.
“An officer used an axe to smash a window to create an escape path for the driver, before swimming him to the pontoon.
“Other officers have provided first aid before ambulance staff were on scene a short time later.”
Graham commended the courage of Maritime Unit officers.
“Our team have encountered a risky and life-threatening situation that was rapidly evolving in front of them,” he says.
“They have not hesitated to respond and without a doubt have helped saved a life.”
Police said the man was taken to hospital and was receiving support.