WELLINGTON/SYDNEY (REUTERS) - New Zealand on Tuesday (Aug 18) ruled out the possibility that a coronavirus outbreak in its biggest city of Auckland came from frozen food items or freight, as it reported 13 new cases.

Investigations suggested the virus had not come through chilled services or material arriving from overseas at an Americold cold-storage facility in Auckland where one of the recently infected individuals worked, health officials said.

"Seems clear now that the possibility is being ruled out from that investigation," Director General of Health Ashley Bloomfield told reporters.

The origin of the latest outbreak is still unknown, and transmission through the environment in the cold storage was one theory being considered.

New Zealand has fared far better than most countries during the pandemic, but an abrupt resurgence of Covid-19 last week in Auckland prompted the government to extend a lockdown for the city's 1.7 million residents until Aug. 26, while social distancing rules are in place in other towns and cities.

An additional 13 cases were reported in the community on Tuesday, taking the total number of active cases to 90, of which 69 were linked to the outbreak in Auckland.

New Zealand's total number of coronavirus infections now stands at 1,293, with 22 deaths.

New Zealanders celebrated when the country passed 100 days without any community transmission earlier this month.

With an election due in mid-October, Prime Minister Jacinda Ardern is keen to remind voters of her government's track record on fighting the virus.

"Every other single country in the world has experienced resurgence. We went longer than many, our outbreak is certainly not as significant as what we are seeing in Vietnam, in Hong Kong, in South Korea or in Australia," she told state broadcaster TVNZ.