A fresh outbreak of COVID-19 in Auckland has prompted political parties to suspend their campaigns.

As part of the government response, Ms Ardern placed the country's biggest city in a "level three" lockdown, making a traditional campaign impossible.

The rest of the country is at "level two", capping gatherings at 100 and seeing the return of social distancing.

The restrictions will be in force until Wednesday, August 26 - just 10 days before advance voting is scheduled to start for the poll.

Ms Ardern has been urged by Opposition Leader Judith Collins to consider pushing the election back to November, or even next year, but the PM says she is yet to decide.

"Today, the most important focus for cabinet and indeed for myself ... was what we do with alert levels," she said.

The Electoral Commission has been granted a budget increase and says it has been planning for an election under level two restrictions.

That includes double the number of polling places as the 2017 election and a push on advance voting to minimise lines.

Ms Ardern has pushed back the dissolution of parliament, planned for last Wednesday, to next Monday, to allow breathing space for the call.

Until the writs are issued, the decision on election day belongs to the PM.

After that, the commission can decide whether conditions are unsafe for the election to proceed.

While Ms Collins wants the poll to be deferred, Greens co-leader James Shaw has urged Ms Ardern to go ahead with the September 19 date if possible.

"So you kick it out by a month ... what happens if there's another outbreak?" he asked.

"There's actually no certainty at all. The only way to be certain is to stick with the date that we've got.

"It's tough. It's tough on families, it's tough on businesses and it's tough on political parties attempting to campaign. We just have to adjust to the reality that this is a global pandemic."

With caps on gatherings and handshaking strangers, Mr Shaw ruled out employing skywriters to get out the Greens' message.

"That sounds like a vey high carbon approach to campaigning ... it is primarily about moving to digital," he said.

Australian Associated Press