A 63-year-old who chased an intruder at his property was savaged by a police dog that attacked the wrong man.

"It was a dirty big black German shepherd that came screaming towards me, with 12 foot of lead hanging off it, no dog handler ... and chewed the living Christ out of my left leg," Brett Abraham said from Auckland City Hospital yesterday.

Last night, Mr Abraham was recovering after two hours of surgery to open up and clean out the bite wounds - one on his upper left thigh, the other his lower leg.

"They have to cut dog bites open even bigger to wash them out properly," he said. "They say they don't normally stitch them up because they are likely to go all septic."

The drama began when a security light at Mr Abraham's Woodhall Rd home in Epsom went on at 2.48am yesterday.

"I remember looking at the alarm clock ... I got up and went outside but there was no sign of anyone, which I thought was strange, but then I saw a bike leaning on the fence against the property."

Mr Abraham understood the intruder had followed a local girl home and she had phoned police. The man had then hidden his bike down Mr Abraham's driveway.

But with no sign of anyone nearby, he went back to bed, until the light came on again.

This time, his wife Jean spotted the man running away. Mr Abraham said he gave chase, screaming at him to stop, and was attacked by the dog.

Inspector Mark Hall, of the Auckland dog section, said a dog handler saw the intruder cycling towards him and ordered him to stop.

"He failed to do so and the dog was released and commanded to apprehend the offender," he said. "Unfortunately, the offender swerved away from the dog and the dog has continued on and bitten the victim."

An Independent Police Conduct Authority inquiry is under way.

Mr Abraham has been told he will have more surgery on Monday. He had to cancel flights and motel bookings for a nine-day South Island holiday that was due to start yesterday.

Mr Abraham was furious about the incident and critical of the police response. "He [the police officer] didn't shine a torch on it [his leg], he didn't know if my femoral artery had been bitten through, he didn't have a clue."

Mr Abraham said he dragged himself up the driveway to his wife and daughter, who phoned 111. St John staff told him to apply pressure to the wounds until the ambulance arrived.

However, Mr Hall denied the dog handler failed to help Mr Abraham.

He said the officer went straight over to him and helped him to the house, before heading back to his van for a medical kit.

Mr Hall said the handler then returned to the house, helped keep pressure on the wounds, and waited for the paramedics. In the meantime, other police had caught the intruder.

"[Police are] obviously sympathetic to the plight of the victim who [had] been injured through no fault of his own ... It's a terrible event."

Mr Hall said the officer involved was an experienced dog handler with a mature dog, which was under control before and during the incident.