Two of the cases were said to involve the L452R mutant strain, while the test result of the remaining case was still pending.
The three include two domestic workers, aged 28 and 34, from Indonesia and the Philippines, as well as a 30-year-old man who arrived from Pakistan.
All of them were asymptomatic and have been inoculated with the Sinovac and Convidecia vaccine respectively.
The city has recorded 12,276 coronavirus cases so far.
Britain's Queen Elizabeth carried out her first official engagement on Tuesday since spending a night in hospital and being ordered to rest by her doctors.