The emptying of the flats was to allow officials to determine whether the vent pipes were linked to the spread of the disease after at least one home in the building was found with improperly sealed piping.

Chuang said more residents might be evacuated with the inspection of pipes on the 1st to 28th floors ongoing.

The 59-year-old patient lived in flat 13 on the 34th, or top, floor of Heng Tai House, above a couple infected earlier. The couple, who lived in flat 13 on the 32nd floor, had joined a tour group to Egypt between February 27 and March 7.

As a precaution, all residents in flats numbered 13 and 14 from the 29th to 34th floor of the block were asked to vacate their homes and quarantined at Chun Yeung Estate in Fo Tan.

Infectious disease expert Professor Yuen Kwok-yung said on Saturday that said one possibility for transmission from the couple was through faecal matter from the 32nd-floor flat under the so-called “wake effect” of the wind.

Yuen said the particles could have travelled through a vent pipe, which has an opening on the roof of the block, and become aerosolised, whereupon the wind might have carried the aerosols back to homes near the top floors, including the 34th.

While officials have said the top floors should be safe as long as the vent pipe openings were at least two to three metres from the roof, Yuen said the highest floors could be contaminated by particles emitting from the pipe, outside the No 13 flats, after officials found it was shorter than usual.

Vincent Ho Kui-yip, former president of the Hong Kong Institute of Surveyors, said the law only stated the distance should be at least one metre.

“It could be safer if the opening of the vent pipe is even farther away, but we need further analysis to prove that,” he said.

A spokesman for the Housing Department said the piping design of Heng Tai House was compatible with the relevant legislation.

While cleaners were seen sanitising the block on Sunday morning, some residents decided to move away temporarily on their own accord.

“We are not living in flats numbered 13 or 14, but we are still worried because we have kids,” said a father of two surnamed Choi.

Meanwhile, the seven patients newly confirmed in Hong Kong on Sunday were aged between 29 and 61 and had travelled to Japan, France, Germany, Austria, United States and Canada.

One of them was a 35-year-old male Hongkonger, who lives in Wah Ming Estate in Fanling, and visited Hokkaido in Japan on a ski trip with friends from February 26 to last Wednesday, when he landed home on flight CX560 from Osaka. He was in hospital on Saturday after developing a fever.

Two Frenchmen, aged 37 and 39, were diagnosed on Sunday after returning from Paris on flight CX260 after a ski trip.

The fourth case is a male foreigner, 29, of unknown nationality, who visited Germany and Austria earlier this month. Chuang said in Austria the man had been in contact with a friend, who later tested positive for the virus, without wearing a mask.

After learning of his friend’s condition, Chuang said the man checked into The Harbourview hotel Wan Chai for a few days on his arrival in the city on flight LH796 from Frankfurt.

Chuang said hygiene officials had been asked to help disinfect the hotel and quarantine any staff who might have entered his room. The Post has approached the hotel for comment.

Among the confirmed patients revealed late on Sunday were an expat couple living at Kellett View Town House on The Peak. They had travelled to Toronto in Canada, as well as New York and Boston in the United States.

The husband, 58, developed fever and cough last Tuesday, before arriving in Hong Kong on flight CX811 with his 61-year-old wife on Wednesday, before both were admitted to Ruttonjee Hospital in Wan Chai.

The seventh of Sunday’s confirmed cases was a 32-year-old man, who the authorities have said was possibly infected locally.

The man joined a tour to Tunisia from February 24 to March 2 and then visited Britain and Spain with friends until March 9, returning to Hong Kong on March 10.

Citybus later confirmed that the man is one of its drivers, and drove routes 90, 96 and 98 from March 11 to March 13, while wearing a mask. The company said it would disinfect the buses he drove, and stops he visited.

As of Sunday, 58 coronavirus patients were being treated at 13 public hospitals in Hong Kong, which had recorded 84 cases of recovery and four fatalities.

Meanwhile, Lion Rock Group, a listed company that provides printing services in Hong Kong, said its executive director Lau Chuk-kin had tested positive for the virus, adding there would be “no material disruption to the business”.

Lau is likely to have been recorded as the city’s 134th case, who was confirmed infected on Friday and had visited Britain between February 27 to March 8.

The company also said its headquarters in North point had been thoroughly cleaned.