The US Open is set to be the first tennis grand slam to operate at full spectator capacity for its duration since COVID-19 became a global crisis.

Tournament organisers said on Thursday that the major, which was played behind closed doors in 2020, would not impose reduce attendance measures this year.

"New York is back, and so are the fans," a statement on the tournament's website said. "The 2021 US Open will welcome fans back to the USTA Billie Jean King National Tennis Center at 100 per cent capacity for the two-week tournament."

Mike Dowse, chief executive of the United States Tennis Association (USTA), said: "We are extremely excited to be able to welcome our incredible fans back to the US Open this year.

"While we were proud that we were able to hold the event in 2020, we missed having our fans on-site, because we know that they are a large part of what makes the US Open experience unlike any other.

"Indeed, the challenges presented by the pandemic were tough on us all, but our sport came together like never before and tackled each challenge head on."

Dowse added: "Our sport surged in the toughest of times, and this year's US Open promises to be an unforgettable celebration of the game, those who play it, and those who revel in it."

The tournament added that it would follow all COVID-related guidelines, although its intention clearly is to run the major in as normal a manner as is possible.

The US Open's announcement came on the day tickets went on sale for the upcoming Wimbledon championship, which begins on June 28. The grass-court slam was cancelled last year.

Wimbledon will operate at a 50 per cent attendance restriction for much of its duration, although the weekend of the finals is due to see Centre Court at 100 per cent capacity.

The French Open functioned with a vastly reduced number of tickets available in both its 2020 and 2021 editions, compared to previous years.

The Australian Open in February capped spectator numbers at 30,000, although a snap lockdown in Melbourne meant there were no crowds for five days midway through the event, with Rod Laver Arena then limited to approximately 50 per cent capacity for the closing stretch of the event.

Naomi Osaka and Dominic Thiem won the women's and men's singles titles at the 2020 US Open, and this year's tournament runs from August 30 to September 12.