Prime Minister Jacinda Ardern says the Government won't ban criticism of religious groups, but is reviewing whether New Zealand laws go far enough in stopping violence against them.

Justice Minister Andrew Little has asked his ministry to work with the Human Rights Commission to look into whether New Zealand's laws sufficiently balance issues of freedom of speech and hate speech.

It comes in the wake of the Christchurch terror attacks and concerns from religious groups about extremist language from people inciting violence against them.

While laws prohibit the incitement of racial disharmony, Little says the same sanctions don't apply on grounds of religious faith.

Ardern said the work was extremely important, but needed to be dealt with carefully as to not inappropriately limit freedom of expression.

"I think probably that people will agree that is a gap in our legislation and so that is something the Minister is working his way through, really carefully though," she told The AM Show.

"This is an area where we need to be really cautious about balance freedom of speech, but also where that speech tips over into a space where it becomes potentially violent and harmful."

She said the review wouldn't lead to people's ability to criticise religious groups being banned, but instead it would consider if enough was being done to stop people threatening violence towards them.

"There is a very big difference between criticism and even sharing views that people necessarily wouldn't agree with, there is a very big difference between that and language which is designed to incite harm against others.

"That is something that we jealously guard in our legislation and our democracy, but at the same time, of course, people would expect that if you are trying to incite violence and potentially murder against groups of individuals based on their beliefs, no one in New Zealand would think that was okay either, so it is just making sure we get that balance."