Several rescue helicopters cannot now land at hospitals because of Civil Aviation rules.

The regulations require rescue helicopters to have twin engines if they are to fly over hospitals.

This affects six rescue helicopters based in Tauranga, Hamilton, Rotorua, New Plymouth, Palmerston North and Nelson.

They cannot land unless it is a life-and-death situation, 3 News reported.

The $4 million single-engine Taranaki rescue helicopter does not comply with hospital helipad safety regulations and cannot use its hospital base, which cost the community $280,000 to build. It now has to land at a nearby site.

"The risk is made up of both probability and consequence - and the consequences of an engine failure of a single-engine helicopter going into a built-up area could be catastrophic," said CAA spokesman Bill Sommer.

To comply with the regulations, the services will have to replace their helicopters with an expensive twin-engine model such as Wellington's Westpac helicopter.

The CAA says the operators have had well over a year's warning.

Taranaki Community Rescue Helicopter Trust chairman Mike Masters said the red tape and relocation had caused a delay in response time to emergencies.

"I can't say whether it will put lives at risk ... but there is always that potential."

The operators say it could put their contracts with ACC in jeopardy

Helicopter operators said the rules were ridiculous. Modern-day, turbine-powered helicopters were so efficient and safe there had not been an accident involving single-engined helicopters carrying passengers.

"They're picking on something that's not a problem," said one pilot.