New York City will become the first major U.S. city to require proof of COVID vaccination for customers and staff at restaurants, gyms and other indoor businesses as the country enters a new phase of battling the highly contagious Delta variant.

The announcement is the latest in a string of initiatives aimed at encouraging more residents to get vaccinated as the Delta variant spreads in the nation's most populous city.

"We know this is what's going to turn the tide," de Blasio told a news conference.

About 60 percent of all New Yorkers have received at least one dose of the COVID-19 vaccine, according to city data. But certain areas, largely poor communities and communities of color, have lower vaccination rates.

The policy will be enforced starting Sept. 13. It is similar to measures taken in France to curtail the spread of coronavirus.

As part of the initiative, the city is creating the "Key to NYC Pass" to provide proof of vaccination to workers and patrons at fitness centers, restaurants and entertainment venues, the mayor said.

The announcement comes on the heels of several steps taken by city officials to encourage still reluctant residents to get their shots, including a mandate for city employees to get vaccinated or face weekly testing.

The highly contagious Delta variant has been wreaking havoc across the United States, leading to a worrisome increase in infections and hospitalizations.

(With input from agencies)