A police constable is being treated for hypothermia after swimming to the rescue of a would-be car thief who fled into the cold waters of Lake Rotorua.
Police were called to a house in Kawaha Point at about 4am when a home owner caught a man breaking into a car on his driveway.
The alleged offender threatened the home owner with a pipe wrench after being confronted, police said.
An officer with a police dog chased the man 3km through properties and reserves in Kawaha Point before catching him in the backyard of a house near Lake Rotorua.
Police said the man then jumped down a steep bank and into Lake Rotorua, which has a current temperature of about 9.5 degrees.
Despite the dog handler's calls to return to shore, the man headed into deeper water where he began to struggle and show signs of hypothermia.
He went underwater at least twice before a police constable could swim out and carry him back to shore.
The man was taken to Rotorua Hospital by ambulance and treated for hypothermia and water in his lungs.
His rescuer was also taken to hospital suffering from hypothermia.
Inspector Ed Van Den Broek commended staff for rescuing the man after his "poor decision" to head into the lake.
"This is an excellent piece of police work."
A Hamilton man, 29, has been charged with attempted unlawful taking of a motor vehicle and aggravated assault over the incident.