New Zealand’s human rights commission has announced a new campaign to combat racism, warning that action was needed to prevent overt discrimination becoming as widespread as in Australia and other nations.

Race relations commissioner Dame Susan Devoy said the rapid growth of ethnic diversity in New Zealand was putting pressure on Kiwis’ world-renowned tolerance.

In an open letter, Devoy said although “overt racism is not as widespread as it is in, say, Australia”, taking a proactive approach would help New Zealanders reassert their position as world leaders in race relations.

Each year the human rights commission received roughly 400 complaints of racist behaviour, although the vast majority of incidents went unreported, she said.

Of these 400 complaints, the majority concerned discrimination towards Asian people, and were largely centred around employment issues, including not being granted leave for religious holidays and jobs being advertised as open only to those of a certain ethnicity.

Devoy said although many Kiwis would be “appalled” by reports of casual prejudice, Maori New Zealanders knew the island nation of 4.5 million had “always had a problem with racism”.

“We are often held up as a model of healthy race relations to the rest of the world, and the Treaty of Waitangi is widely admired,” Devoy told the Guardian.

“But I don’t want New Zealand to follow behaviour we are seeing in other parts of the world where hate speak, overt racism and divisive talk is becoming normalised.”

The human rights commission is asking New Zealanders to come forward and tell their stories of experiencing racism in New Zealand – be they victims, defenders, bystanders or abusers.

A web platform has been established to record people’s stories but Devoy said the commission was open to “any form” of communication, including letters, telephone calls or multimedia expressions. Translators would be available if needed.

Devoy said that with a national election scheduled next year and record levels of immigration she did not want to see migrants being blamed for every “issue and problem” in the country.

“New Zealand is a small country at the bottom of the world. Overt racism is becoming increasingly widespread overseas and we don’t want that narrative coming into New Zealand. I don’t want to be the only Kiwi calling out racist behaviour, I want other people to be calling it out too.”

Dr Chris Sibley, an associate professor in the school of psychology at the University of Auckland is a lead researcher in the New Zealand attitudes and values study, which has surveyed the same 20,000 New Zealanders every year for seven years.

The survey measures how “warm” participants feel towards other ethnicities in New Zealand. The study has found the participants felt most negatively towards Muslim people, more warmly or neutral towards Asian people, increasingly warmer towards Maori and Pacific people, and most warmly towards Pakeha (white) people.

“We are a largely peaceful and tolerant nation but for people who do experience everyday or casual racism there is still huge room for improvement. It can be extremely damaging.”

Sibley said warmth towards Asian people was “very slowly improving” over the seven years, but warmth towards Muslims remained low.