SYDNEY -- New Zealand will again suspend its quarantine-free travel bubble with Australia for at least eight weeks in response to the spread of the delta coronavirus variant on the continent, Prime Minister Jacinda Ardern said Friday.

"This is not a decision we have taken lightly but it is, we believe, the right one," Ardern told a news conference.

"Now is the time for a suspension to ensure New Zealanders aren't put at undue risk from COVID-19 and to ensure we retain our hard-won gains," she added.

The prime minister noted in a press release that there are multiple outbreaks in Australia that have forced three states into lockdown.

Australia and New Zealand each imposed tight border controls and stay-at-home orders last year as part of their COVID-19 response, helping to keep their COVID-19 cases relatively low.

They agreed to mutually accept travelers without quarantine, and the travel bubble launched April 19. More than 200,000 people had flown between the two countries in the months since the arrangement was set up, Ardern said.

But delta cases have multiplied in Sydney, Australia's largest city, since mid-June. New Zealand temporarily shut down the travel bubble on June 26.

New Zealand reopened it in July to certain parts of Australia for those with proof of negative COVID-19 tests. The new shutdown took effect Friday night.