Christchurch gun owners have handed over their weapons in exchange for cash in the first of more than 250 planned buyback events around New Zealand after the government outlawed many types of semi-automatics.

Police say they paid more than $NZ200,000 ($191,000) to 68 gun owners in the first couple of hours of the Saturday event.

New Zealand lawmakers in April rushed through new legislation to ban so-called military-style weapons after a lone gunman killed 51 people at two Christchurch mosques in March.

The government has set aside more than $NZ200 million to buy back weapons such as AR-15 style rifles, although many gun owners remain unhappy with the compensation on offer.

Under an amnesty, gun owners have until December to turn over their now-banned weapons.