New Zealand's Maori king has refused to meet Britain's Prince William during a tour next month, with his office saying he is "not a carnival act" for visiting dignitaries.

Prime Minister John Key expressed disappointment at the snub.

The meeting would have involved the prince visiting King Tuheitia during his 7-16 April trip to New Zealand with wife Catherine and baby son George.

However, King Tuheitia's office rejected the offer, arguing that the 90 minutes allotted for the visit to the Maori leader's base in the North Island was not long enough for proper protocols to be observed.

His representatives also slammed the "faceless bureaucrats" who organised the itinerary, accusing them of adopting an inflexible approach when dictating the terms of the proposed visit.

The Maori leader decided not to agree to the meeting and sent a personal letter to the British royals outlining his reasons, his office said in a statement.

"A senior rangatira [chief] noted that the king and the Kiingitanga [the movement he leads] are not some carnival act to be rolled out at the beck and call of anyone," the office said.

"And nor should we be prepared to compromise our tikanga [customs] to fit into a pre-determined schedule. It would have put the king in an impossible situation."

Mr Key said 90 minutes was a "quite generous" amount of time, given the British royals' busy schedule, and it was a shame the visit to the Turangawaewae marae, or meeting place, would not go ahead.

"It's rather disappointing because I think Prince William would have enjoyed going to Turangawaewae," he told New Zealand’s TV3.

"But it was King Tuheitia's people who said 90 minutes is not long enough. If you look at the programme, there are very few places where they're there for an hour, let alone 90 minutes.

"Of course he has to travel, he has to fit different things in. So in the end, King Tuheitia's people said: 'If you can't make it longer than 90 minutes then don't come' - so they're not coming."

King Tuheitia is descended from the first Maori King, Potatau Te Wherowhero, who was appointed in 1858 by various North Island tribes, who wanted a single figure to represent them in the way that Queen Victoria was felt to represent New Zealand's white settlers.

The position does not have any constitutional status or legal powers in New Zealand, but carries symbolic importance for some Maori.

The current king worked as a truck driver before his coronation in 2006.

The British royal couple will base themselves in Wellington and tour extensively through New Zealand, before visiting Australia.