Prime Minister Malcolm Turnbull has called ethnic and community leaders to try to contain a growing backlash against sweeping changes to Australia's race-hate laws, while terrorism experts have warned they could play into the hands of violent extremists.

Mr Turnbull on Tuesday said the laws had lost credibility and that fixing them would require the removal of legal prohibitions on people's right to "offend, insult or humiliate", contained in section 18C of the Racial Discrimination Act, while making it illegal to "harass" or "intimidate" a person.

According to people familiar with the phone calls, Mr Turnbull explained why his government had proposed the changes, its commitment to multiculturalism in Australia, its support for strong laws prohibiting vilification and the need to strengthen freedom of speech protections.

But a broad array of ethnic groups, united under the banner of the Coalition to Advance Multiculturalism, released a letter condemning the changes as "utterly shameful and at odds with the principles of multicultural Australia".