A local resident, she was among eight new cases reported yesterday, three of which were imported, four from unknown local sources and one pending classification.

The 46-year-old returned via Shenzhen Bay Port on April 6 after being in Dongguan for a year.

Under the Return2HK program, she was exempted from 14-day quarantine after testing negative 72 hours before crossing the border.

She lives at Sun Ching building in Tsuen Wan and had been working as a cleaner at Nina Hotel since April 10.

She was tested as required on the second, 12th and 19th days upon arrival. Her 12th day sample on Saturday came back positive.

Centre for Health Protection's Chuang Shuk-kwan said the cleaner had been exposed to many people and believed she contracted the infection in the SAR.

She was responsible for cleaning 10 to 11 rooms on the 42nd floor of the hotel. More than 40 people, including cleaners and guests, will be sent to quarantine.

Another new case was a 56-year-old woman who took the express rail from Fujian to Guangdong and returned via Shenzhen Bay Port on April 6.

As Return2hk only waives quarantine for Hongkongers who have not been outside Guangdong for the past 14 days, she had to observe a 14-day home quarantine.

She stayed at a friend's place at Fu Yung Building in Tsuen Wan. On Saturday, she developed a headache and tested positive.

"Since Fujian has not reported cases recently and she has been living with a friend, we are testing the friend and a dozen others sharing the same subdivided units who could be her source of infection," Chuang said.

The woman had taken two doses of the Covid vaccine in the mainland, but did not know which brand she took.

Four vaccines have been approved for use in the mainland - two by Sinopharm and one each by CanSino and Sinovac.

Another unknown source case yesterday was an Indonesian helper who arrived on March 20 and had stayed in Tsim Sha Tsui's Ramada Hong Kong Grand until April 9, before starting work at her employer's home at Yung Lai House, Yau Tong Estate.

She had not stayed on the same floor as the three people cross-infected with the South African strain and it is believed she could have contracted the virus from the community.

The other two unknown source cases were a 57-year-old female clerk living in block four of Belvedere Garden phase two in Tsuen Wan and a 47-year-old construction worker from a site on Renfrew Road, Kowloon Tong.

The cases came as Singapore announced shorter quarantines for arrivals from Hong Kong to seven days from 14, starting Friday, to pave the way for a travel bubble.