"The Electoral Commission, via the Ministry of Justice, has advised me that a safe and accessible election is achievable on this date," Ardern told a press conference.
This short delay gives the commission more time to prepare including freeing up facilities for early voting during school holidays, she said.
Moving the date by four weeks also gives all parties a fair shot to campaign and delivers New Zealanders certainty without unnecessarily long delays, Ardern said.
"With the re-emergence of COVID-19 in our community these are not ordinary times and so while the decision as to the election date sits with me, I spoke with all party leaders to seek their views," she said.
"COVID-19 will be with us for some time to come. Continuously pushing out an election does not lessen the risk of disruption," the prime minster said, adding she would not change the election date again.
This decision gives all parties time over the next nine weeks to campaign and the Electoral Commission enough time to ensure an election can go ahead, Ardern said.
Advance voting begins on Oct. 3, she added.