New Zealand has announced its first locally transmitted coronavirus infections in more than 100 days and issued a stay-at-home lockdown order for the country's largest city.

After receiving global praise for its success containing the virus, Prime Minister Jacinda Ardern said four cases had been detected in a single family in Auckland from an unknown source.

“After 102 days, we have our first cases of Covid-19 outside of managed isolation or quarantine facilities ... we have all worked incredibly hard to prevent this scenario,” she told the country in a televised address.

“We have also planned and prepared for it.”