By Wenxin Fan, Frances Yoon and John Lyons

Hong Kong's finance sector was roiled Thursday by a coronavirus outbreak that emanated from fitness centers in the city, with large banks, brokerages and asset managers vacating some offices and employees rushing to get tested for Covid-19.

HSBC Holdings PLC told employees to vacate an entire floor of its headquarters, located in the city's Central district, after an employee tested "preliminarily positive" for the virus, according to people who saw an emailed notice from the British-headquartered bank. In Hong Kong, a second test from a government laboratory is done to confirm the result of an initial positive test.

Other employees who work in HSBC's iconic tower, which has close to 50 floors, were asked to avoid coming to the office unless necessary, the memo said. The affected person had worked on the 22nd floor of the building, which is undergoing deep cleaning.

At Credit Suisse AG, an employee who had recently been to a gym tested preliminary positive for the virus, according to people familiar with the matter. The individual worked on the 91st floor of a skyscraper across Hong Kong's Victoria Harbour. The Swiss bank occupies 12 floors in the 108-story building in Kowloon, called the International Commerce Centre, and the 91st floor includes some of its trading activities.

Some staffers on the same floor as the affected individual were told to go home on Wednesday afternoon and that the office would undergo deep cleaning, one of the people said. On Thursday, the employees were asked to get tested for Covid-19 before returning, the person added. The same building also houses the offices of Morgan Stanley and other global financial firms.

An employee of BNP Paribas also had a positive test after visiting the gym, but the French bank didn't vacate its office.

Mutual fund giant T. Rowe Price Group Inc. closed its office in Hong Kong's Central district Thursday for deep cleaning, according to a person familiar with the matter. "We don't have any employees that tested positive as of today," a Hong Kong-based spokeswoman for the Baltimore-headquartered asset manager said Thursday.

Hong Kong, a crowded city with a population of about 7.5 million, has kept coronavirus cases relatively low compared with the rest of the world, thanks in part to widespread mask-wearing and social-distancing rules that have limited outdoor and restaurant gathering sizes to four and under. The city has reported a little over 11,000 confirmed cases since the pandemic began, including roughly 200 deaths.

But while the numbers are tiny compared with London, New York and other big cities, Hong Kong's government has taken a zero-tolerance approach to outbreaks and has an elaborate track-and-trace system to identify individuals with the virus and their close contacts. Schools across the city have been only partially open even though daily case numbers were, until recently, in the single digits or teens for weeks.

The current outbreak, which is rippling through Hong Kong's expatriate community, affected several fitness centers. It started at a small gym called Ursus Fitness that is known for so-called strongman workouts, where gym goers lift heavy objects like kegs and tires.

Ursus, in a Facebook post on Thursday, said that one of its staff members felt unwell and took a rapid Covid-19 test that day. Another employee, who was asymptomatic, tested positive soon after.

Since then, around 50 individuals have been linked to the gym cluster, including employees, customers and their close contacts. Dozens more who visited have been tracked down and sent to government quarantine facilities for up to 14 days.

Hong Kong's Center for Health Protection said Thursday that more than 240 people visited the gym between March 1 and March 10 and it is trying to locate all of them.

The outbreak has also caused the closures of multiple international schools, after some teachers and parents of students visited the gym and either tested positive or were awaiting their test results. Youth rugby leagues in Hong Kong, a popular activity comparable to U.S. Little League Baseball, also suspended practices on Thursday night.

Write to Wenxin Fan at Wenxin.Fan@wsj.com, Frances Yoon at frances.yoon@wsj.com and John Lyons at john.lyons@wsj.com

(END) Dow Jones Newswires

03-11-21 0824ET