The Prime Minister summoned two military helicopters and their crews on an eight-hour journey, instead of driving 90 minutes to a boat launching ceremony.

John Key used the helicopters during a whirlwind day of travel to cut out the road trip between Blenheim and Kaikoura, where he was launching a new Whale Watch boat.

The prime ministerial use of Royal New Zealand Air Force craft has been a vexed issue in the past - Helen Clark was attacked by Act Party members for using a Beechcraft King Air and an Orion.

Now the former prime minister's colleagues are raising flags about the behaviour of her successor, suggesting Key stick to the road rather than using up Air Force time and money.

On Thursday, Key set off from Auckland to Wellington, where he collected two staff, his diplomatic protection squad team and Associate Conservation Minister Kate Wilkinson.

The team then caught a commercial flight to Blenheim where two helicopters were waiting just after 9am to take them to Kaikoura. The helicopters are based at Ohakea, north of Wellington, and would have had to leave about 8am to meet Key and his team.

The trip from Blenheim to Kaikoura is about 90 minutes by road - yet Blenheim pilots estimate it would have taken 30 minutes by Iroquois, giving the PM just a two-hour saving on a return trip.

However, the return trip did not go through Blenheim - and that was why the Air Force was required to bring an extra helicopter along, flying empty apart from its crew.

The Prime Minister and team were returning directly to Wellington and the return flight across the Cook Strait is considered unsafe for a single aircraft to make alone. An Air Force spokesman said the Iroquois was a single-engined helicopter and needed to be shadowed by a second helicopter in case it crashed.

Key arrived in Kaikoura about 10am to an hour-long powhiri at the Kaikoura Winery, then launched the Whale Watch boat, Wawahia. He went out on a whale-watching tour before returning to shore for lunch.

Kauahi Ngapora, chief operating officer of Whale Watch Kaikoura, said watching the air crafts land and take off was awesome. "That doesn't happen often down here," he said. "We could hear them before we could see them. They came out of the mountains and it was awesome."

The Prime Minister's group returned to Wellington about 3.30pm.

A spokeswoman for the Prime Minister said Key had a hectic day, and flew straight back to Auckland from Wellington for a function with the Governor General and Prince Edward. "The reason he flew from Blenheim to Kaikoura was to get into Kaikoura for the maximum amount of time. He would have thought this was appropriate for the day - to attend what he considered to be an important event."

Labour defence spokesman Pete Hodgson said the use of the helicopters by Key and his entourage was "highly inefficient". He said there was a contracted VIP driver in Blenheim - and a backup in Nelson - who were available to carry Key and his team along the South Island roads.

But Key's spokeswoman said the Blenheim and Nelson drivers were generally not used to transport the Prime Minister, for training and security reasons, so two cars would have had to be brought up from Christchurch.

Hodgson also accused Key of a lack of transparency over his own travel at a time when details of MPs' spending is being made more open and the Prime Minister's coalition partners are copping flak for their own spending.

He said the arrangement with the Air Force which allowed VIPs to use military aircraft was not publicly accounted for - unlike "every time I take a taxi chit".

"The Prime Minister has a transport system that is not covered by the transparency system that applies to the rest of us."

An Air Force spokesman said he was unable to get details of how many hours of VIP travel had been used. The Air Force budgets 25 hours of VIP flights in the Iroquois each year - and Key's spokeswoman said little of that quota had been used.

Two vociferous opponents of military travel by Helen Clark, Act leader Rodney Hide and his deputy Heather Roy, did not comment on Key's helicopter flight.