New Zealand social media has been inundated by US pro-gun tweets since the Christchurch attacks, and new data analysis by the Herald shows many of these were from accounts intended for harassment.

Since the terrorist attack in Christchurch, there have been nearly 9000 tweets about gun control in New Zealand, retweeted almost 90,000 times in total. Two-thirds of these came from users in America, based on analysis of their activity patterns. Some were in support of the Government's gun reforms, but the majority were pro-gun voices describing it as a "gun grab" or an attempt to "disarm" New Zealanders.

More than 9000 of the users involved described themselves using the hashtags #NRA (National Rifle Association), #2A (Second Amendment, the part of the US Constitution relating to guns) or #MAGA (for President Donald Trump's campaign slogan "Make America Great Again"). Many tweeted at the Police and the Prime Minister's accounts directly, accusing them of being socialists and dictators.

Why does gun control in New Zealand inspire such passions in America?

"I think what the Prime Minister has done stands in such stark contrast to how the debate to address gun violence usually go in the United States. It represents a real threat to how the National Rifle Association operates," says Chelsea Parsons, Vice President for Gun Violence Prevention at the Center for American Progress, a thinktank in Washington DC.

"The NRA and the gun lobby in the US ... promote this narrative of futility, which is 'we shouldn't consider new gun laws because gun laws won't work'," says Parsons. "We're already hearing from the advocacy community here: 'Why can't our leaders do what Prime Minister Ardern is doing in New Zealand? Why can't we have that?'."

Parsons says that the NRA is already active overseas, recently sending their experts to Mexico to testify at a senate hearing on gun control legislation. The scope and the speed with which New Zealand enacted new gun controls is likely to put us on their radar.

John Hart, a Wairarapa farmer who made international headlines last week when he voluntarily handed in his semi-automatic rifle to the Police for destruction, was the biggest single focal point for the online harassment, with more than 8000 tweets directed at him personally over the past fortnight.

Hart posted the original tweet after handing over his rifle the Monday after the attack.

"It kind of went nuts," says Hart, "within a couple of hours I realised it was getting much much bigger, because it was getting comments from all over the world." Local media coverage followed that evening, but he woke up on Tuesday to find that his Facebook page was overrun with comments by strangers.

The comments ranged from saying that New Zealand was a dictatorship and that he was leaving his family defenceless, through to asking "what kind of man are you" and saying that he should cut off his own penis. "It was just this absolute trash fire," says Hart, "just incoherent rage."

Of the accounts that tweeted at Hart during this period, more than 100 have already been deleted or suspended by Twitter. But many more appeared to be accounts specifically created for harassment. These are often new accounts whose sole activity is to jump into existing conversations and hurl insults at the participants. They tend to be new because they are often suspended or deleted, and then the person behind them creates a new account.

But the threat comes from more local sources as well. Hart found his photo and email address being posted on a New Zealand gun blog, with a comment encouraging other readers of the blog to email Hart. The moderator of the blog responded to this with: "Please be respectful. Of the piece of s***."

Despite this, Hart says he intends to continue as he has. "If you didn't [know] that these people are probably bots and or bad you could easily go 'oh my god the world hates me'. You can see how that constant tirade could actually grind someone down. I guess I'm a little more meta about it. The minute you give them room in your head you've given them the victory."