Police are hunting the killer of a North Shore doctor who was knocked off his bike by a hit-and-run driver.

Ian Graham Robinson, from Mairangi Bay, was riding on Peak Rd near Helensville when a Toyota ute hit him on Wednesday morning.

His cycling buddy - also a doctor - tried desperately to treat him at the scene, but he never regained consciousness and died in hospital on Thursday night.

The vehicle hit Dr Robinson, 62, from behind, flinging him over the handlebars.

Sergeant Mike Colson of Helensville said yesterday that more than 48 hours after the killing, investigators were no closer to finding the Toyota.

"The road he was hit on is now used as a bypass for the main highway, so the driver could have come from North Shore or West Auckland or anywhere.

"We are hoping to narrow down the search a hell of a lot more."

Mr Colson said police would not know if the driver was acting recklessly until he or she had been spoken with. "If the driver was aware of the accident, he had an obligation to stop. They could be looking at [a charge of] careless driving causing death.

"If we find there are more sinister aspects then it would be manslaughter. But we cannot establish anything until we track [the driver] down."

Detectives interviewed Dr Robinson's friend last night to get more details about the vehicle, described as cream or off-white with a discoloured fibreglass hard cover.

Dr Robinson biked Peak Rd regularly, on a circuit that finished with a cup of coffee with fellow cycling enthusiasts.

He was a keen runner and former member of the Owairaka athletics club, but took up cycling about 10 years ago after a tropical disease contracted while on holiday affected his heart.

After a serious bike accident two years ago in which he broke his hip, his wife Lin let him continue on the condition he did not cycle alone.

Colleague Kim Bannister said it was good Dr Robinson had a friend with him when the accident happened.

"It wasn't enough to save his life, but they were there to try first aid and give him a chance at living."

Dr Bannister said patients wept as they learned of Dr Robinson's death.

"Our world has been turned upside down here. It is devastating, to have him plucked away like this."

Dr Robinson's death, less than three weeks after four cyclists were mown down and injured - one critically - on Auckland's Tamaki Drive, has fuelled controversy about the rights of competing road users.

Cycle Action Auckland chairman Mark Bracey said there was an urgent need to change attitudes of drivers, who obtained licences too easily, without being required to take third-party insurance.

"It's an issue of the culture of driving. I'm a motorist as well as a cyclist, and I get tail-gated. I find it hard to drive on the road - there's just this sort of Wild West attitude."

Cyclist John Carter said Peak Rd, with its hills and corners, was on the training route of his group, the Pickled Pedallers, for the annual cycle race around Lake Taupo, and members were determined not to deviate from it during a 95km ride tomorrow.

"In fact, it will be a show of solidarity [with Dr Robinson] for us to go out and do Peak Rd."

Transport Agency data shows 10 cyclists were killed last year and 185 were seriously injured.

More than 12,000 people have signed a petition urging the Government to make it illegal for vehicles to pass cyclists with less than 1.5m to spare.

DANGEROUS ROADS

Wednesday: Dr Ian Robinson victim of a hit-and-run near Helensville. Killed.
September 26: Greg Paterson is one of four people hit by a vehicle that fails to stop on Auckland's Tamaki Drive. Critically injured.
September 18: Frank van Kampen, Kapiti Coast, knocked down by a motorist, who fails a breath-alcohol test. Killed.

- additional reporting: James Ihaka, Mathew Dearnaley