WELLINGTON, Sept 14 (Reuters) - Prime Minister Jacinda Ardern asked New Zealanders on Tuesday to get vaccinated as soon as possible, as it was the only way to beat the spread of coronavirus and see curbs lifted in the biggest city of Auckland. Tuesday"s 15 new infections in New Zealand were a drop from Monday"s figure of 33, but about 1.7 million people will stay in lockdown in Auckland until next week, as the government battles to hold down a cluster of the highly infectious Delta variant. "The vaccine is the best tool we have in our toolbox and our ticket to greater freedom," Ardern told a news conference. "The more people who are vaccinated, the fewer restrictions you have to have." Auckland"s lockdown has shut schools, offices and public places, with people allowed to leave home only for exercise or to buy essential items. In the rest of the country, the lockdown was lifted last week. New Zealand had been largely virus-free for months until a Delta outbreak forced a snap lockdown on Aug. 17. It has infected 970 people so far, most of them in Auckland. The lockdowns and international border closure since March 2020 have been credited with holding down COVID-19, but a slow vaccination effort has spurred criticism for Ardern. Just 34% of the population of 5.1 million have been fully vaccinated. To boost the programme, New Zealand has bought doses of Pfizer-BioNTech (PFE.N) vaccine from Spain and Denmark. "There is nothing holding us back in Auckland when it comes to vaccines," Ardern added. "There"s capacity to administer 220,000 doses of vaccine in the region this week." Vaccine buses will begin plying this week to reach more people, she said.