New Zealand's new gun laws get final assent to take effect

New Zealand's governor general on Thursday formally signed into effect sweeping gun laws outlawing military style weapons, less than a month after a man used such guns to kill 50 people and wound dozens at two mosques in Christchurch.

Governor General Patsy Reddy signed the bill as police said a gun buyback program will be announced to collect the now-banned weapons.

The weapons will be illegal starting at Thursday midnight, but police said a brief amnesty program will be in effect until details of the buyback are announced.

"For people who find themselves now in possession of a prohibited firearm, we ask you to please notify us," Police Deputy Commissioner Michael Clement said.

"The collection of firearms will occur at a later stage. " He added that "for now, there is an amnesty in place and we ask people to please notify us," he added.

Anyone who retains such a weapon now faces a penalty of up to five years in prison.

Exemptions allow heirloom weapons held by collectors or weapons used for professional pest control.