The lockdown, which extends through Wednesday, is the first in New Zealand in six months and represents a significant setback in the nation's largely successful efforts to control the virus.New Zealand’s largest city of Auckland has begun a three-day lockdown following the discovery of three unexplained coronavirus cases in the community.Health officials said Monday the cases were of the more contagious variant first found in Britain and that genome testing hadn’t linked them to any previous known cases.Prime Minister Jacinda Ardern announced the lockdown after an urgent meeting with other top lawmakers in the Cabinet.She said they decided to take a cautious approach until they find out more about the outbreak.The lockdown, which extends through Wednesday, is the first in New Zealand in six months and represents a significant setback in the nation’s largely successful efforts to control the virus. It has also forced a delay in the America’s Cup sailing regatta.New Zealand had successfully stamped out community spread, and many people elsewhere in the world looked on in envy as New Zealanders went back to work and began attending concerts and sporting events without the need to wear masks or take other precautions.Indeed, Ardern on Sunday had planned to attend the Big Gay Out, an Auckland festival that celebrates the rainbow community and attracts tens of thousands of people. She ended up canceling those plans and returning to Wellington to manage the outbreak.“I’m asking New Zealanders to continue to be strong and to be kind,” Ardern said at a hastily arranged press conference. “I know we all feel the same way when this happens. We all get that sense of Not again.’ But remember, we have been here before and that means we know how to get out of this again, and that is together.”New Zealand’s greatest vulnerability has been at the border.New cases are regularly caught among returning travellers, all of whom are required to spend two weeks in quarantine. Despite precautions, there have been several times when the virus has leaked out from the border before being controlled again, and officials are trying to determine whether that’s happened again.In the latest case, an Auckland mother, father and daughter caught the disease. Officials said the mother works at a catering company that does laundry for airlines, and officials are investigating whether there is a link to infected passengers. Officials said the woman hadn’t been going aboard the planes herself.The rest of New Zealand outside of Auckland has also had restrictions imposed, including limiting crowd sizes to 100.“We are gathering all of the facts as quickly as we can, and the system that served us so well in the past is really gearing up to do so again,” said COVID-19 Response Minister Chris Hipkins.He described the cases as new and active.“New Zealand has kept COVID-19 contained better than almost any other country,” Hipkins said. “But as we have kept saying, there is no such thing as no risk.”New Zealand, with a population of 5 million, has reported a total of just over 2,300 cases and 25 deaths since the pandemic started.The country has been hosting the America’s Cup sailing regatta. Racing was due to continue on Wednesday in the Prada Cup challenger series, but organizers have announced that a postponement will be necessary. Italy’s Luna Rossa Prada Pirelli leads Britain’s INEOS Team UK 4-0 in the first-to-seven series. The winner will then take on Emirates Team New Zealand for the America’s Cup.