In what have been described as "uncommon" cases by health authorities, two babies have been infected with the HIV virus by their mothers.
The Centre for Health Protection announced the cases on Tuesday during its review of the HIV/AIDS situation in Hong Kong in the first quarter of 2019.
The two mothers tested negative for HIV during pregnancy, but were infected later.
"Without knowing her own HIV status, the mother could have infected the baby by breastfeeding or during childbirth," said Dr Kenny Chan, a consultant with the Centre for Health Protection.
The last mother-to-child transmission for a local born baby was in 2015.
The centre said there were 146 new cases of HIV infection in the first three months of the year, raising the total number to 9,861 since records began in 1984.
Dr Chan said sexual transmission remained the major mode of HIV transmission. He stressed the importance of consistent and proper use of condoms to reduce the risk of contracting the virus.
During the period, 22 new cases of AIDS were reported.