Trade Me does not allow the sale of military style semi-automatic weapons, parts which could change an 'A' category firearm into a military style semi-automatic weapons, pistols, or restricted weapons, Macdonald said.
Macdonald said he believed trading guns on Trade Me provided safe, transparent and traceable sales between licensed owners, which was better for the country than "many of the alternatives".
"But it is clear public sentiment has changed in relation to semi-automatic weapons and we acknowledge that, which is why we're putting this ban in place.
"There is a bit of work involved in doing this but we will have these listings removed later today."
Over the weekend, the crowd in attendance at a vigil at Auckland's Aotea Square cheered loudly when Attorney-General David Parker said the Government would ban semi-automatic rifles.
He warned of a global rise of extremism.
"There is a dimming of enlightenment in many parts of the world," he said.
"How can it be right for this atrocity to be filmed by the murderer using a go-pro and live-streamed across the world by social media companies?
"How can that be right? Who should be held accountable for that?"
Parker's comments come after Prime Minister Jacinda Ardern's earlier remarks that New Zealand's gun laws would change.
Speaking to media in Wellington this morning, Ardern stressed that "now was the time for change."
Ardern said five guns were used by the primary perpetrator, including two semi-automatic weapons, and two shotguns.
"The offender was in possession of a gun licence," Ardern said.
She said the guns were purchased in December last year.
