The news emerged late on Tuesday in a memo to staff, while notices placed at the 1mn sq ft building informed visitors it would be closed indefinitely.
Shortly after the internal notice was issued, the government announced that anyone who had visited any floor at the bank’s office tower on Queen’s Road in Central since March 2 would be subject to a mandatory Covid-19 test.
Two cases of Covid-19 have been confirmed at HSBC in recent days, as a cluster centred on a gym in Sai Ying Pun popular with financial industry professionals continues to spread.
A third positive case, involving a worker based on a different floor, is understood to have triggered the closure. The 38-year-old is an IT engineer who developed a runny nose on March 10. He was last at work on Monday.
Two floors of the building had previously been subject to compulsory testing notices.
In total, 22 residential building, workplaces and other venues were placed under compulsory testing notices issued at midnight on Tuesday.