Governments across the Asia-Pacific region are tightening restrictions on daily life and travel as slow vaccination campaigns have failed to halt the spread of infections with the Delta variant of Covid-19.

New Zealand Prime Minister Jacinda Ardern ordered a nationwide lockdown Tuesday following the first Covid-19 case in the community since February. The lockdown will last three days in most of the country and seven days in Auckland, the largest city.

Japan said Tuesday it would extend a state of emergency in Tokyo and other cities to Sept. 12 and add several regions to the emergency zone. The measures had been set to expire Aug. 31. Hong Kong said Monday it would tighten quarantine rules for people returning to the city after foreign travel, and it added the U.S. to a list of high-risk countries.

Australia’s two largest cities, Sydney and Melbourne, are locked down, and on Sunday authorities expanded the lockdown to the entire state of New South Wales. In Melbourne, playgrounds are closed, an overnight curfew starting at 9 p.m. has been imposed and construction sites can operate at only 25% of capacity.

“At the moment we have a steady number of cases who are out in the community each day, and an increasing number of mystery cases, and we need to get ahead of that,” said Brett Sutton, chief health officer of Victoria state, where Melbourne is located.

Hong Kong has mandated long quarantines for arrivals to the city.

Photo: bertha wang/Agence France-Presse/Getty Images

The additional restrictions are coming in countries and regions that have generally been more successful than the U.S. and Western Europe in battling Covid-19. Some have imposed mandatory restrictions on public movement, while others such as Japan have requested voluntary steps and relied on widespread mask-wearing.

The news isn’t all bad, thanks to vaccinations. Deaths in Japan, where vaccination of people over 65 is largely complete, are running at about a quarter of the peak May level, and South Korea also has fewer deaths than the previous peak.

Still, the highly contagious Delta variant, spreading among populations that are generally less than half vaccinated, has led to unprecedented outbreaks.

Japanese government minister Yasutoshi Nishimura, summarizing the advice of medical experts, said their message was, “The situation has become close to a disaster” and “If this continues, we will not be able to save lives that we could have saved.”

Dr. Shigeru Omi, the government’s top Covid-19 adviser, said some experts wanted new legislation that could compel businesses and the public to restrict their activities. “We may not get through this just by asking the public to cooperate,” he said.

A normally bustling Bourke Street Mall in Melbourne, Australia, was quiet on Monday.

Photo: Darrian Traynor/Getty Images

Authorities in South Korea, which like Japan is battling its largest outbreak of infections since the pandemic began, said current restrictions banning gatherings of more than two people after 6 p.m. weren’t able yet to suppress infections. That suggested the measures, currently set to end Aug. 22, were likely to be extended or made stricter.

New South Wales, home to Sydney, has recorded 8,654 local coronavirus cases since June 16, when authorities say a limousine driver who transported international flight crew was found to have the Delta variant. The state set a new daily record of 478 daily cases on Monday.

Mr. Nishimura, the Japanese official, said infection clusters were identified in places that hadn’t been previously affected much, such as department stores, hair salons and cram schools where teens attend classes after their regular school.

The Japanese government drew criticism from opposition parties and others for going ahead with the Summer Olympics from July 23 to Aug. 8 during the pandemic. Critics said the event sent the wrong message about the risks of Covid-19 and diverted government attention from vaccinations, while Olympics organizers said there was no evidence that visitors contributed to the infection wave.

Covid-19’s Delta variant is proliferating world-wide threatening unvaccinated populations and economic recovery. WSJ breaks down events in key countries to explain why Delta spreads faster than previously detected strains. Composite: Sharon Shi The Wall Street Journal Interactive Edition

Hong Kong, known for mandating some of the world’s longest quarantine measures, said the U.S., France and Thailand would be added to a high-risk list that includes some two dozen countries, effective Friday. Hong Kong residents returning home from those places must spend 21 days in quarantine at a hotel even if they are fully vaccinated.

Foreign tourists and unvaccinated Hong Kong residents will be barred from entering Hong Kong from high-risk countries. Australia, meanwhile, was moved to medium-risk from low-risk, meaning 14 days of hotel quarantine will generally be required for vaccinated travelers.

“This is a disaster. No hotels are available,” said Desalyn Bowyer, 41, who is in Australia visiting her children, whom she hadn’t seen in 16 months. Ms. Bowyer, who needs to return to Hong Kong for work, is looking for a hotel where she can stay for two weeks. Although she is fully vaccinated, it “means absolutely nothing,” she said.

Hong Kong Chief Executive Carrie Lam said the restrictions were needed to prevent imported cases of the Delta variant, which studies have shown can also be spread by vaccinated people.

Asian nations have generally been slower than the U.S. and Western Europe in vaccinating their populations. In South Korea and Australia, only about one in five people has been fully vaccinated. The figure is about two in five in Japan, compared with half of Americans.

All three countries have taken steps to secure more vaccines from companies including Pfizer Inc. and Moderna Inc. with the aim of getting most people fully vaccinated by late this year.

Meanwhile, public impatience with the progress in containing the spread of Covid-19 is aggravating political tensions. Economic hardship coupled with frustration over the slow pace of vaccinations has contributed to protests in Thailand and the resignation of Malaysia’s prime minister on Monday. Both countries are battling record caseloads of more than 20,000 new infections a day.

A slightly brighter picture has emerged in Indonesia, which has suffered the most severe outbreak among East and Southeast Asian nations. Infections are beginning to decline, although the country is still recording more than 15,000 cases and more than 1,000 deaths each day. The government has limited dining in restaurants and the size of congregations at places of worship on the main island of Java and neighboring Bali.

—Stephen Wright in Wellington, New Zealand, Jon Emont in Singapore and Dasl Yoon in Seoul contributed to this article.

Write to Elaine Yu at elaine.yu@wsj.com, Megumi Fujikawa at megumi.fujikawa@wsj.com and David Winning at david.winning@wsj.com