More than six million people in Victoria, Australia, will enter into a snap lockdown for five days in response to a coronavirus outbreak at a quarantine hotel.

The order came as the Australian Open was being held in Melbourne, Victoria’s capital, but the tennis tournament will continue — without spectators — the authorities said on Friday.

Victorians will be allowed to leave home only for essential shopping, work, exercise and caregiving, and must wear masks whenever they leave home.

But while sports and entertainment venues will be shut down, professional athletes like tennis players will be classified as “essential workers” and allowed to continue their matches.

“There are no fans; there’s no crowds. These people are essentially at their workplace,” Daniel Andrews, the premier of Victoria, told reporters on Friday. “It’s not like the only people that are at work are supermarket workers.”

Tennis Australia said in a statement that it would notify all ticket holders of the changes and continue “to work with the government to ensure the health and safety of everyone.”

The lockdown, which goes into effect at 11:59 p.m. on Friday, comes after an outbreak at a Holiday Inn near the Melbourne Airport that was being used to house returned travelers.

By Friday, 13 people linked to the hotel had tested positive with the new virus variant that first emerged in Britain. In the past 24 hours, five new cases have been identified, bringing the state’s total number of cases to 19.

Describing the lockdown as a “circuit breaker,” the authorities said it was critical to stopping the spread of the variant, which is highly infectious and has outwitted contact tracers before they can contain outbreaks. Similar snap lockdowns in Perth and Brisbane in recent months were successful in quashing infections.

“The game has changed,” Mr. Andrews said. “This is not the 2020 virus.”

He said he hoped Victorians, who endured among the longest lockdowns in the world last year, would work together to prevent the state from entering a third wave of the coronavirus. “We will be able to smother this,” he said.

The order had ripple effects in Australia’s other states, which all announced travel restrictions with Victoria. International flights, excluding freight, into Melbourne were also canceled.