BERLIN — In nations around the world that saw new coronavirus infections decline in recent weeks, spikes in confirmed case numbers have alarmed officials, and sent Australia, Germany, Portugal and South Korea, among other countries, scrambling to respond to resurgent outbreaks.

Within the countries in question, the new flare-ups are mostly rooted in identifiable regions, where officials launched or expanded aggressive containment efforts this week.

German authorities said Tuesday they would impose a new regional lockdown in a district of the country’s northwest to contain an outbreak linked to a meat-processing plant, after more than 1,500 workers were infected. Portugal cracked down on mass gatherings. Australia’s Victoria state re-shuttered several schools. An area in the northeast of Spain reintroduced restrictions. Even New Zealand, which has just 10 confirmed, active cases, tightened border measures as an increasing number of citizens abroad began to fly home.

The swell of responses to outbreaks around the world stood in stark contrast to the U.S. approach. With cases on the rise in nearly half of states and with Arizona, Florida and Texas recording record new case numbers in recent days, states have continued to reopen and the White House has continued to signal its desire for a return to normal.

President Trump has maintained the United States will not shut down a second time, despite a clear spike in infections over the past week in the Southern and Western regions of the country. The number of daily new coronavirus cases remains at a far higher level in the United States than in Europe, where stringent lockdowns have helped to slow the spread of the virus.

In Germany, by comparison, policymakers imposed regional thresholds based on new case numbers or strain on hospital capacity that trigger a snapback in restriction or put reopening on hold. The announcement Tuesday that lockdown measures would be reimposed in a district in northwestern Germany saw this system put to use.

Schools and kindergartens had already shut their doors as the number of cases climbed in recent days. Starting Tuesday, people will only be able to meet with one other person or members of their own household. Gyms, bars, galleries and museums will be closed. Health officials remained optimistic that localized outbreaks could be contained through testing, contact tracing and quarantines.

In some countries, new measures are not yet in place, but rising infection numbers have prompted officials to warn that strict control measures could return in coming days.

The mayor of Seoul said this week that social distancing measures lifted last month may once again be necessary in the metropolis if a second wave of cases linked to a holiday in May continues to grow. Israeli Prime Minister Benjamin Netanyahu urged compliance with social distancing measures on Sunday, warning that the country could otherwise return to lockdowns.

In Lisbon and Seoul, nightlife has faced growing scrutiny, after new outbreaks were linked to clubs, bars or mass gatherings in public.

South Korea has been hit by a second wave of cases, initially expected for fall or winter, said Jeong Eun-Kyeong, director of the Korea Centers for Disease Control and Prevention. Seoul Mayor Park Won-soon warned social distancing measures would need to be reimplemented if cases continued to climb this week or if hospital admissions reached more than 70 percent of capacity.

“If the R-number [reproduction rate] stays at the figure seen 10 days ago, daily new infections are expected to reach around 800 a month later,” he said, according to the Yonhap news agency, urging citizens to wear face coverings and to avoid crowded spaces.

During the initial phase of the pandemic, South Korea only exceeded or came close to 800 new confirmed cases per day twice.

The country avoided full lockdowns throughout its first wave of infections, relying instead on a test-and-trace strategy along with stringent quarantine measures. The country has recorded a relatively low coronavirus death toll, with 281 reported fatalities.

Portugal, which has seen 1,540 confirmed fatalities, has faced fading compliance with social distancing guidance in recent weeks.

The number of young people infected with the virus has spiked since social distancing requirements were eased. Last weekend, police officers dispersed hundreds of people who had gathered illegally.

Restrictions snapped back in some parts of the country on Tuesday in response to the breaches. Limits on the maximum number of people allowed to gather were lowered from 20 to 10 in districts that have seen case numbers rise, among other efforts to crack down on the sale or consumption of alcohol in restaurants or in public.

“The nucleus of the problem is centered in just 15 neighborhoods,” said Portuguese Prime Minister António Costa, according to Reuters.

Officials in the Australian state of Victoria also blamed large gatherings for climbing case numbers.

Over the weekend, officials there already lowered the cap on gatherings following four consecutive days of double-digit rises in infections. As during the first phase of reopening, no more than 10 people can meet in public and no more than five can assemble inside homes.

On Tuesday, officials also closed two primary schools after a flare-up of more than a dozen coronavirus cases prompted concerns about “significant” community spread.

“I know and understand that all Victorians want this to be over,” Victoria State Premier Daniel Andrews said at a news conference, “but we simply can’t pretend the virus is gone, that the virus is somehow not in our state."

His comments echoed a growing rift that has emerged between nations that are doubling down on trying to contain the virus and countries like the United States, where scientists fear economic recovery is being prioritized over virus containment efforts.

Much like Washington, Pakistan’s government has also pushed to further reopen its battered economy this week, even though confirmed cases of the coronavirus have surged. More than 3,600 people have died, according to figures shared by the Health Ministry on Tuesday.

Restrictions meant to contain the pandemic earlier this year drove millions of Pakistanis toward hunger and starvation, putting pressure on the government to change course.

But aid groups are have warned of an increasingly dire coronavirus situation that is forcing hospitals to turn patients away, as shopping malls and most businesses are once again fully operational.

Jennifer Hassan in London, Shaiq Hussain in Islamabad, Teo Armus in Washington and Loveday Morris and Luisa Beck in Berlin contributed to this story.