Maori Party co-leader Pita Sharples says working with the National Party in government is proving at times to be "very difficult and stressful".

His comments - in a hard-hitting speech last night marking Race Relations Day - are the first time the Maori Party leadership has openly expressed such frustration and dissatisfaction with what Dr Sharples described as "tensions" in his party's relations with National.

His speech, however, fell short of saying what his party would do to remedy those tensions or whether the Maori Party was having second thoughts about continuing to support the National minority Government.

If the Maori Party was to scrap the agreement under which it supports the Government on confidence motions, National could still govern with the help of Act.

However, there is also division within Act, with some senior members questioning whether that party's long-term interests and survival are best served by continuing to be linked so closely to National.

Dr Sharples said the Maori Party's agreement with National was an example of leadership in race relations but "it was not always easy".

He cited the Government's refusal to have any designated seats for Maori on the Auckland Super City.

"It seems to me to be poor reward for such a major role played by Ngati Whatua in ensuring the city of Auckland could survive, grow and flourish."

He was "saddened" establishment of the seats had lost out to the politics of the day - a reference to Act, which blocked moves to set them up.

Dr Sharples said the Government's stance on signing up to the United Nations Declaration on the Rights of Indigenous Peoples was another source of tension. While the Government had announced its intention to support the declaration, it had attached a number of caveats.

"I am dedicated to completing this exercise and to pulling back these caveats. I believe adopting the declaration would mean recapturing some of the courage and momentum in advancing race relations that we lost with the Auckland seats."