Prince Charles ponders Lake Manapouri on the South Island during his April 1981 visit to New Zealand.

Prince Charles warned he would make New Zealanders "laugh out the other side of their faces" for repeatedly making fun of him falling off a horse, a letter set to be sold at auction has revealed.

The handwritten note, sent by the first in line to the throne to a friend in April 1981, has been published by British newspaper the Daily Mail.

It reveals that the Prince of Wales was so aggrieved by comments from New Zealanders about footage of him falling off his polo horse that he was determined to seek revenge.

MARLBOROUGH EXPRESS Prince Charles wrote he would make New Zealanders 'laugh out the other side of their faces' during his 1981 visit. He is pictured here greeting crowds in Blenheim.

In Christchurch he wrote: "kindless, fallacious remarks and references about falling off horses are beginning to get through to me.

"It seems as though the main thing they know about me out here! It all increases my determination to make them laugh out the other side of their faces one day!"

The Prince - who was only three months away from marrying Diana at the time - also used the written correspondence to bemoan his royal duties, describing them as "nonsensical rubbish", the Daily Mail reported.

He also criticised the children he had met on his New Zealand tour, writing: "The real problem is keeping up my enthusiasm on each new day because I am beginning to get fed up with the amount of nonsensical rubbish I take all day and every day!"

"If one more NZ [New Zealand] child asks me what it's like to be a prince I shall go demented."

READ MORE: *Charles and Camilla to visit New Zealand in November 2015

*Prince Charles to be given three military titles when he visits New Zealand in November.

The Prince of Wales was mocked during the royal engagements after falling from his polo horse in a dramatic head first tumble while playing in an invitational match at Warrick Farm in Sydney, Australia.

The moment was caught on camera and to New Zealanders became a source of much amusement, the Daily Mail reported.

Prince Charles visited the country on a two-week tour from March 31 until April 12, 1981, during which one of his official duties was to open the Royal New Zealand Police College.

The letter, to an unidentified friend, was dated April 10.

Prince Charles and his wife, the Duchess of Cornwall, are due to visit New Zealand in November where the Prince is due to be given three military titles.

Prime Minister John Key said in July that future visits should occur more regularly than they had in the past to build on the "close and special links" between New Zealand and the royal family.

"I am delighted to welcome them both back to New Zealand," Key said.

"I'm sure New Zealanders will be excited to hear that Their Royal Highnesses are returning, providing another opportunity to meet members of the royal family here in New Zealand."