Health authorities on Friday reported 221 new local Covid cases and said they believe a subvariant of Omicron, BA.2.12.1, is spreading on Hong Kong Island.

At a daily briefing, officials confirmed that four earlier cases all involved the subvariant, adding that there's no clear link between these people and others who are thought to have caught it at a McDonald's in Taikoo Shing.

Albert Au from the Centre for Health Protection said a colleague of one of the four new patients at the Hong Kong Convention and Exhibition Centre in Wan Chai has also come down with Covid.

He said both patients work as cleaners at the centre, but they don't know each other and didn't work together.

However, the doctor said the pair both visited the staff canteen and used the same changing room and officials will look into whether the colleague also has the BA.2.12.1 variant.

"We think the Omicron subvariant BA.2.12.1 is spreading in Hong Kong Island," said Au.

"Among the four new cases, two of them work in Wan Chai. Therefore, we are speculating the subvariant has been leaked to the community through silent cases and further caused a transmission."

He added that dozens of workers at the exhibition centre were being told to take tests.

Meanwhile, officials said a class of around 20 students at DSC International School has been told not to return to school on Monday and to get tested for the virus over the weekend.

This comes after two students and a teacher were reported to have been infected on Friday.

Another student from the same class tested positive a few days ago and officials are investigating whether there's been "small-scale" transmission in the classroom.

Au said since the school is also located in Taikoo Shing, they will investigate whether the students had been to the same places as earlier patients.

Authorities also reported 29 imported cases for the day and said they suspect Covid has spread in a quarantine hotel, Courtyard By Marriot Sha Tin, after three guests who stayed in rooms next to each other tested positive.

The Hospital Authority, meanwhile, said one more Covid patient has died.