New Zealand First MP and Cabinet Minister Tracey Martin says she personally witnessed a National Party MP instructing online "trolls" to attack a political opponent.

Martin will not name the MP, but says she watched him direct a group of supporters on Facebook to personally attack then-Labour leader Andrew Little while they were sharing a domestic flight during the election campaign.

The Internal Affairs Minister recalled the story at an event hosted by Netsafe in Auckland yesterday, saying that she was concerned about the role of social media in manipulating politics here and overseas. Addressing an audience of about 40 people, she said she had never spoken about it publicly.

"During the 2017 election I was on a plane and there was another Member of Parliament sitting in front of me."

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She said she stood up and witnessed the incident.

"... I watched this person in front of me, who was running a group of 15 trolls on Facebook, give them the messages that they needed to start bombarding the other party that they were trying to have an effect on.

"The messages they sent changed the outcome of the election. It wasn't the outcome they were hoping for, but that was what they were attempting to do.

"They personalised the messages to try and get one individual to feel so uncomfortable about their position that they removed themselves from it."

"The messages they sent changed the outcome of the election" - Tracey Martin. Photo / Mark Mitchell

Little stood down as Labour leader just three months before the election following a string of poor poll results, saying that his party needed a campaign uncluttered by questions about his leadership.

Little, who is now Justice Minister, wouldn't comment on the allegations yesterday.

National Party deputy leader Paula Bennett told the Herald that it was "an unusual accusation for a minister to make".

"Perhaps she should focus on NZ First's problems and doing her job instead," Bennett said.

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National has previously been outspoken on cyber-bullying, passing the Harmful Digital Communications Act when it was in Government in 2015.

Martin told the Herald after her speech that she was certain of what she saw on the plane. She told her colleagues about the National MP's actions but did not consider any further action or making a complaint.

"It won't be a shock to anybody that it's a political tool. I wouldn't be surprised if Labour runs similar groups of people.

"But we need to decide whether that's appropriate, because they run personal attacks against either the leadership or individual MPs in the name of politics.

"I don't think it's reasonable or appropriate behaviour for any adult to be creating a group of others to specific target a single individual. If a young person did that, we'd all be calling it bullying."

Bullying within Parliament has come into sharper focus in recent months. Speaker Trevor Mallard launched an independent inquiry into bullying and harassment within Parliament in November.

The review coincided with allegations of bullying behaviour against former National MP Jami-Lee Ross. Those allegations prompted the National Party to review its own practices to ensure a safe working environment.

Labour MP Meka Whaitiri was also stood down after an allegation that she shouted at and grabbed one of her staff.