Prime Minister Jacinda Ardern says it's unfortunate that incidents like one in which a woman carrying a sword allegedly damaged her electorate office have come to be expected.

A 57-year-old woman was arrested after Ardern's Mt Albert office was damaged about 8.20am on Thursday.

In a call to the Herald newsroom on the same day, a woman claimed she had used a sword to smash a window 10 times before shoving a smoke bomb into the office.

Ardern subsequently told reporters in a press conference in Antarctica where she has been visiting that incidents like this were happening regularly at her electorate office but were not "okay".

"Unfortunately, one thing I have observed is we have had some fairly consistent activity over the past couple of years," Ardern said.

"That does not make it okay."

No staff members were inside the office when it was damaged.

A woman claims she used a sword to punch a hole in the window of PM Jacinda Ardern's electorate office. Photo / Dean Purcell

"Number one for me is making sure the wonderful people who work with me are safe," Ardern said.

"And I was thankful to hear they weren't present at the time."

• PM's office attack: Staff evacuated after sword used to damage Jacinda Ardern's Auckland office
• Woman arrested after sword attack on Prime Minister Jacinda Ardern's electorate office

She said such incidents were "extremely upsetting" because staff in electorate offices deserve a safe place to work and they are ultimately there to "assist people".

"They help them with housing issues, immigration issues, welfare issues," Ardern said.

The incident also raised fresh concerns about the safety of politicians in the lead-up to the next election campaign.

Ardern today said she couldn't predict whether incidents like Thursday's would become more or less frequent in the lead-up to the next election.

Damage done to Prime Minister Jacinda Ardern's office this morning. Photo / Dean Purcell

However, Deputy Prime Minister Grant Robertson said last month politicians might have to increasingly take official security teams around with them.

That was especially up for consideration during the next election campaign when MPs typically do walkarounds in the electorates to meet voters, Robertson said.