The Department of Health said on Sunday that it's following up some vaccination irregularities, including the case of a man who received mixed coronavirus vaccines.
It said in a statement that the 32-year-old man went to a private clinic for a Sinovac jab late last month, without telling the doctor he had received a BioNTech jab two weeks earlier.
The private doctor reported the incident to the department after checking the man's vaccination record on the government's eHealth System.
The doctor also told the man not to receive another dose of Covid vaccine.
But the man went on to get a third jab - this time BioNTech - a week ago, against the private doctor's advice and without disclosing his full vaccination history to the staff at the inoculation centre.
The department said it has been monitoring the man's condition.
It said that it had so far not received any report of any "adverse events following mixed doses of vaccination".
It added that medical workers must check people's vaccination records before inoculating them.
Separately, the department said nine non-Hong Kong residents have been given their first dose of Sinovac vaccine.
"In view of the health of the vaccine recipients, the DH will... notify the concerned private doctors to provide a second dose to them in order to complete the vaccination course."
It added that it has reminded doctors to only administer the vaccine to eligible people.
The department also said some residents who received their first Sinovac shot at private clinics did not complete the vaccination process by getting their second dose, and urged them to contact the department or community vaccination centres.