Prime Minister Jacinda Ardern on Saturday declared that she would push ahead with tightening the laws around gun control in the country where there are an estimated 1.5 million firearms, about one gun for every three people.

It's alleged that the mosque accused - Australian white supremicist Brenton Tarrant - had a firearms licence and was in possession of five guns.

Changes to the laws have previously been rejected, but Ms Ardern is determined to make it happen.

"We cannot be deterred from the work we need to do on our gun laws in New Zealand," she said on Sunday.

"They need to change, regardless of what activity may or may not have happened with gun retailers."

Cabinet will also receive briefings on Monday from security agencies on the Christchurch massacre and national security.

Tarrant was not on any watch list in New Zealand, where he lived in Dunedin, or Australia.

Members of parliament will pay tribute in the house on Tuesday.

"Once appropriate statements have been given we will adjourn for the day."

Ms Ardern said options and timing for national commemorative services were being considered.

Condolence books will be open at parliament on Monday as well is at the national library.

Australian Associated Press