NEW YORK -- New York City will soon require proof of COVID-19 vaccinations for anyone who wants to dine indoors at a restaurant, see a performance or go to the gym, Mayor Bill de Blasio announced Tuesday, making it the first big city in the U.S. to impose such restrictions.

The new requirement, which will be phased in over several weeks in August and September, is the most aggressive step the city has taken yet to curb a surge in cases caused by the delta variant. People will have to show proof that they have had at least one vaccine dose.

"The only way to patronize these establishments indoors will be if you're vaccinated," de Blasio said. "The goal here is to convince everyone that this is the time. If we're going to stop the delta variant, the time is now."

The Democrat said some details still need to be worked out, including rules affecting children under 12, who are not yet eligible for any of the approved vaccines. The policy will go into effect on Aug. 16 but inspections and enforcement won't begin until Sept. 13 -- the week the city's public schools reopen for fall.

During a Tuesday news conference, President Joe Biden said he supported New York City's move and said other cities need to give "the authority to those restaurants or businesses to say: 'In order to come in, you have to give proof that you're either vaccinated or you can't come in."'

De Blasio has focused on getting as many New Yorkers vaccinated as possible while resisting calls to mandate masks indoors, as several cities and counties in California have done.

He said vaccination cards will be accepted as proof of inoculation, along with state and city apps.

De Blasio said Monday he was making "a strong recommendation" that everyone wear a mask in public indoor settings but stressed that the city's "overwhelming strategic thrust" remained getting more people vaccinated.

Asked Tuesday about a mask mandate, de Blasio said all options were on the table but reiterated the city's policy is "vaccine-centric."

"Right now what we want to nail is people getting vaccinated, and, very bluntly, showing that life is much better when you're vaccinated," he added. "You have more freedom when you're vaccinated, and you have a lot less, you have fewer choices, fewer opportunities if you're not vaccinated."

The mayor announced last week that city employees would be required to get vaccinated by mid-September or face weekly testing, and he has offered a US$100 incentive for city residents who get inoculated.

De Blasio said Tuesday that he did not think checking vaccination status should be too difficult for businesses, which already have to take tickets or show diners to a table.

Some disagreed.

Seongmin Jun, the manager of Dear Han Cafe in Queens, wondered how he would check vaccination cards while handling the periodic rush of patrons and serving as the cafe's only barista.

"Will customers get offended for checking if they got COVID vaccinations? I mean I don't know how to do that, or even if I will have time to do that," Jun said.

The coffee shop opened just months before the pandemic spread early last year.

"They're making it too hard for businesspeople," Jun said, but acknowledged something has to be done to get the virus under control. "I get what they are trying to say, but there must be another way to reduce the cases of COVID."

Sean Ogs, manager of the nearby Woodside Cafe, said he was "floored" when he heard the news about the new vaccination mandate.

"We've already been in a struggle. I don't know how I'm going to deal with it," Ogs said. "It's going to be extra work. It'll make things impossible."

Woodside Cafe customer Debbie McCarthy, who is unvaccinated, said she was turned away over the weekend from several establishments that had already begun requiring proof of vaccinations from patrons.

"I'm a little shocked they would do that," said McCarthy, who said she recovered from COVID-19 a few months ago and believes her natural antibodies will protect from future infections. "Why are they so afraid of people who haven't been vaccinated? I think we should have a choice."

Scientists recommend vaccination for people who have had the virus, saying it's unclear how long immunity without vaccination for those who have recovered would last.

Andrew Rigie, executive director of the NYC Hospitality Alliance restaurant group, said he supports the new policy to ensure "that New York City does not revert to restrictions and shut down orders that would again absolutely devastate small businesses that have not yet recovered from the pandemic."

The Five-Borough Chamber Alliance agreed that the mandate was a "complicated decisions," but said it was "worthy of support for protecting public health and keeping the city on the path to full economic recovery."

Fitness studio owner Bill Zanker said he supports the policy as well, even though it comes as another hurdle after a long coronavirus shutdown.

"We've got to encourage people to get vaccinated. ... We're happy to enforce that," said Zanker, the CEO of GRIT BXNG, a Manhattan studio that offers boxing-related workouts and a full bar. "Unfortunately, it will affect the business again."

The studio had been open for just seven months before the pandemic shutdown began in March 2020. Since reopening this past May, GRIT has checked patrons' vaccination status, offering some inoculated-only classes where people could go without masks while unvaccinated people had to take other classes and cover their faces, he said. About 25 per cent of the patrons are unvaccinated, he said.

Major performance venues including Broadway theaters and the Metropolitan Opera have already announced that vaccinations will be required for patrons.

About 66 per cent of adults in New York City are fully vaccinated, according to official data.

On Monday, the U.S. reached the president's goal of getting at least one COVID-19 shot into 70 per cent of American adults -- a month late and amid a surge by the delta variant that is overwhelming hospitals and prompting renewed pandemic regulations around the country.

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Associated Press writer Jennifer Peltz contributed to this report.