One of the country's most gruelling cycling races is under the spotlight after a rider suffered serious injuries in a pile-up on a winding Coromandel Peninsula road at the weekend.

Witnesses at the 192km K2 race have accused a utility truck driver of cutting off a bunch of more than 100 riders on Saturday morning, to avoid collision with an oncoming milk tanker after overtaking them ahead of a blind bend on the Kuaotunu hill heading north from Whitianga.

They said that caused a chain reaction in which bicycles spun into one other, throwing Auckland rider Brett Burton into the path of the tanker.

Mr Burton, 43, was flown by Westpac rescue helicopter with suspected head and spinal injuries to Auckland City Hospital, where he was yesterday reported to be in a stable condition.

But Inspector Earle McIntosh, of the police northern communications centre, said serious-crash investigators had attended the scene.

Mr McIntosh said comments he could not recall making to the Herald on Sunday, which have caused a storm among cycling advocates, were not intended to judge the circumstances of the crash.

The Sunday paper quoted him as saying: "The cyclists were using the road as if they owned it and came round a blind corner and met a milk tanker."

But he told the New Zealand Herald yesterday that police along the course had been very concerned about the behaviour of some cyclists in using the full width of the road at various stages of both the K2 race and a shorter version between Coromandel township and Tairua.

"It was a huge concern for the police involved in that operation.

"One officer followed a bunch for 10 to 15 minutes out of Whitianga and they were on both sides of the road."

He did not know whether that was the case at the crash scene, but acknowledged that even if it were, it would have been no excuse for dangerous driving by any motorists.

Although he understood the race was a "fairly well-run event", there had been similar problems in previous years with cyclists not following pre-start safety briefings.

The event's Coromandel-based organisers did not return calls yesterday, but two witnesses among about 500 participants in the main race sent email accounts to the Herald blaming the ute driver's actions.

Duncan Milne said he was cycling ahead of the crash but heard it and "turned around to see the guy who hit the [milk] truck spinning out from the side of it.

"It was a horrible sight," he said.

"The ute had come from quite a way back, as we could hear a car horn blasting for some time before it passed us on a blind corner at the front of the bunch.