More than $208m New Zealand dollars (£108m, $136m), have been set aside to compensate owners of semi-automatic weapons which were banned following the attacks.
The ban was agreed by parliament in April, weeks after the shootings.
In March, a gunman killed 51 people at a mosque and Islamic centre during Friday prayers.
How will the buy-back work?
The scheme, which only applies to licensed guns, will last six months meaning people will have until 20 December to hand in their weapons.
"The buy-back has one objective - to remove the most dangerous weapons from circulation," Minister of Police Stuart Nash said.
"Police have detailed plans in place for the next step, which is the collection of firearms from the community. It will be a huge logistical exercise and is expected to get under way in mid-July."
The new gun laws agreed in April ban military-style semi-automatic weapons and parts that can be used to assemble prohibited firearms.
The money set aside will compensate owners up to 95% of the original price of their weapons.
Police estimate that around 14,300 military style semi-automatic weapons would be covered by the new legislation.
So far, almost 700 weapons have already been handed in before the buy-back scheme was launched and around 5,000 have been registered by owners for the police to collect.
What happened in Christchurch?
On 15 March, Australian Brenton Tarrant, a self-proclaimed white supremacist, attacked the Al Noor mosque and the Linwood Islamic Centre in Christchurch.
He is charged with the murder of 51 people, 40 counts of attempted murder and one terrorism charge in New Zealand's deadliest peace time mass shooting.
The gunman, armed with semi-automatic rifles, is believed to have modified his weapons with high-capacity magazines so they could hold more bullets.
The suspect pleaded not guilty to all charges and is expected to face trial next year.
In 2016, New Zealand Police estimated that there were 1.2 million legal firearms owned by civilians - that equates to around one for every four people.