New Zealand's Parliament on Wednesday passed sweeping gun laws that outlaw military style weapons, less than a month after mass shootings at two mosques in the city of Christchurch left 50 people dead and dozens wounded.

A bill outlawing most automatic and semi-automatic weapons and banning components that modify existing weapons was passed by a vote of 119 to 1 in the House of Representatives after an accelerated process of debate and public submission.

The bill needs only the approval of New Zealand's governor general, a formality, before becoming law on Friday.

Prime Minister Jacinda Ardern spoke emotionally during the bill's final reading of the traumatic injuries suffered by victims of the March 15 attacks, whom she visited in Christchurch Hospital after the shootings.

"I struggle to recall any single gunshot wounds," Ms Ardern said. "In every case they spoke of multiple injuries, multiple debilitating injuries that deemed it impossible for them to recover in days, let alone weeks. They will carry disabilities for a lifetime, and that's before you consider the psychological impact. We are here for them."