Prime Minister Jacinda Ardern has confirmed she was the good Samaritan who paid for a mother's groceries after a supermarket mishap.

The Auckland mother-of-two went to pay for her groceries at the supermarket checkout - only to realise she had left her wallet at home.

Ardern was behind her in the queue and paid for the woman's purchases herself.

A reader who alerted the Herald to the act of kindness said Ardern was a "leader like no other".

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"What a wonderful gesture," he said.

In a Facebook post, the mother wrote, "Just when you think Jacinda Ardern couldn't get any more lovely, low key and authentic.... she goes and pays for your groceries at the supermarket, because you've got your shopping, have two kids with you and are about to put it all back as you forgot your wallet".

The woman said she tried to tell her children who had paid for their groceries but all they cared about was how silly she was for forgetting her wallet.

Speaking to media today, Ardern confirmed she had paid for a mother's groceries when asked about it.

When asked why, Ardern replied: "Because she was a mother".

The NZ prime minister's salary is $471,049.

Speaking to reporters his morning, Ardern was asked about comments made by Hamilton City councillor James Casson, who was slammed for social media posts about New Zealand's response to the terror attacks and for calling refugees "scum".

In the now-deleted Facebook post, the former police officer criticises the Government's speedy ban on semi-automatic firearms, the ban on possessing copies of the alleged gunman's manifesto and a widespread bid to avoid use of his name.

Casson also made a post on his personal Facebook page in 2016, prior to being elected, calling refugees "scum" after the terror attacks in Nice, France.

Ardern said she "strongly disagreed" with Casson's comments but conceded he was an elected official and people were able to take their own view on what he said.

She would be meeting with Hamilton mayor Andrew King, but it was unlikely they would discuss any of the city's councillors.

During the press conference, Ardern also touched on the gun law reform taking place.

"The principle of this legislation is very straightforward," she said after questioning about concerns the law changes were being rushed.

"What I've heard is an overwhelming consensus for the principle of this legislation, which is to permanently ban military style assault weapons and rifles."

"Given there is such support for that we are moving quickly to remove them," she said.