New Zealand's gun lobby has begun a fundraising campaign to fight a nationwide ban on military-style semi-automatic weapons in the wake of the Christchurch mass shooting.

The Fair and Reasonable Campaign was launched by the Council of Licensed Firearms Owners (COLFO) in response to what it says are the "rushed changes" to New Zealand firearms laws. It wants to raise public awareness about the "unintended effects" of the new laws.

Fifty-one people were killed in the March 15 terror attack and legislation was introduced just one month later banning the ownership of most semi-automatic weapons, including the AR-15 assault rifle used in the attack. Some pump action shotguns and large capacity magazines that hold more than five cartridges have also been declared illegal.

A gun buyback scheme was officially started on July 13 and the government has set aside 208 million U.S. dollars to compensate licensed gun owners who hand in their weapons. There is also a "no questions asked" amnesty which allows unlicensed people to surrender firearms without any compensation.

The buyback will pay up to 95 percent of the wholesale value of weapons according to their age and condition, but COLFO says that many gun owners are concerned that they won't get fair compensation. The organization aims to raise several hundred thousands of dollars to mount a legal challenge that seeks full compensation for the loss of their hobby, sport and lifestyle.

The New Zealand Police are holding more than 250 firearms collection events throughout the country over the next three months. However some gun clubs have indicated that they will conduct a "silent" protest and hold back their banned weapons which COLFO says that "the risk that people who want to comply will postpone it until too late is real."

Almost 8,000 weapons have so far been registered for surrender by gun owners, but Deputy Police Commissioner Mike Clements says "we just don't know the answer to how many guns there are actually in total."

According to COLFO, 260,000 weapons are affected by the new law and it believes that the potential cost to retrieve them could be as high as one billion U.S. dollars.

The buyback and amnesty will end on December 20 and anyone found in possession of an illegal weapon after that date will face a jail term of up to five years.

Police Minister Stuart Nash is also taking a hard line and says "I have sent a very clear message to the Police Commissioner that I expect Police to enforce this ban and go after those who have not handed in weapons or registered to hand in weapons."