A New Zealander claims that he went to the same rifle club as the Christchurch gunman; he alarmed the police by recalling what he saw there.

In a furious rant on Facebook, former soldier and long range shooting instructor Pete Breidahl said he visited the Bruce Rifle Club in Milburn around the time mosque attack suspect Brenton Tarrant, a licensed gun owner, went there.

Breidahl said he went there for one shoot and was "horrified" by what he saw. According to Breidahl, he had serious concerns about the mental stability of some members of that club, who were talking about a "zombie apocalypse" and "homicidal fantasies".

He added that he saw confederate flags there — a symbol of the American South which is commonly associated with white supremacy.

Breidahl reported the club to an arms police officer but his claims appear to have fallen on deaf ears.

Bruce Rifle Club vice president Scott Williams confirmed that the suspected attacker was a member of the club. "I think we're feeling a bit stunned and shocked and a bit betrayed, perhaps, that we've had this person in our club who has ended up doing these horrible things," Williams was quoted as saying by newspaper Otago Daily Times.

He added that Tarrant seemed "as normal as anyone else'' and was reticent about his beliefs about Muslims.

On Friday, 28-year-old Australian gunman and self-described terrorist Brenton Tarrant murdered 50 people at two mosques in Christchurch, injuring dozens of others.

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New Zealand's Prime Minister Jacinda Ardern told reporters on Saturday that he had legally obtained the five weapons, including two semi-automatic rifles, used in the mass slaying. He is said to have received an A-Category gun licence — a standard one — in November 2017.

She promised that the government would amend the gun laws. According to the current gun laws, one can obtain a licence legally through an application process, which includes a background check and a written safety test.