The number of New Zealanders with 'no religion' has officially surpassed the number of people who identify as Christian in New Zealand, with a secular advocacy group calling for fewer concessions to be given to Christians.

Newly released data from the 2018 Census shows that 48.59 per cent of New Zealanders have 'no religion' - up from 41.92 at the 2013 Census.

The number of people identifying with a Christian faith has fallen from 47.65 per cent in 2013 to 37.31 per cent this year.

The numbers continue a trend line which has been observed over several recent Census counts.

A graph illustrating New Zealand Census data of those identifying as Christian and those identifying as having no religion. Source: Statistics NZ data/1 NEWS graph

In a press release today, Humanist New Zealand - a secular advocacy group - said the numbers suggest it's time to re-think the concessions and privileges afforded to Christians.

Humanist New Zealand president Jolene Phipps said that "Christianity has a privileged position in public policy today that is out of step with modern New Zealand".

"From parliamentary prayers, to classrooms 'closing' during the school day so that Christian groups can run religious instruction, the concessions awarded to religious organisations clash with human rights and our concept of a free and fair society," Ms Phipps said.

"In our hospitals, 10 Christian churches get 100 per cent of the funding for chaplaincy, pastoral and spiritual support from the Ministry of Health.

"Religious groups are awarded charity status and tax exemptions just for promoting religion.

"Non-religious people need more recognition, support, services, and representation. We want to work together to ensure our voices are heard."

The 2018 Census numbers also show rising numbers of people identifying with other religions.

The number of Sikhs has more than doubled, from 19,191 in 2013 to 40,908 in 2018.

The number of Muslims or those practising Islam has risen from 46,149 in 2013 to 61,455 in 2018.