Health authorities said on Thursday that they are concerned about the Covid-19 case of a 22-month-old toddler who is in critical condition, with a government pandemic advisor repeating calls for parents to get their children inoculated against the coronavirus.

Professor Lau Yu-lung told a daily press briefing that the patient had developed a fever, cough and some twitching the night before, and was sent to Eastern Hospital.

Lau noted that she likely caught the virus from her older sister, who earlier tested positive through a rapid antigen test.

The toddler was being treated in intensive care, he said, adding that she's suspected of developing encephalopathy.

Lau again urged parents to get their kids vaccinated against Covid as soon as possible.

"From what I could gather, in terms of a total body knowledge, these two vaccines are effective for children under three years of age to reduce severe cases and deaths and complications arising from Covid-19 infections," he said.

"The whole matter still needs to be discussed thoroughly, seriously, by all the members of the JSC (joint scientific committee) next week. In the meantime, the only thing we can do is to call [on] our parents in Hong Kong to take your children for the vaccination as soon as possible if it's available for you."

Health authorities reported 4,638 local infections and 248 imported cases for the day.

They said 1,384 patients were receiving care at hospitals, including 155 new admissions.

Five more Covid patients, aged between 56 and 100, have died.

Separately, the Hospital Authority announced tougher testing requirements for visitors of public hospitals.

From August 1, all visitors – including recovered Covid patients – must take a PCR test and provide a negative result within 48 hours of entry.

They currently can opt to provide either a negative PCR test result within 48 hours before entry, or a negative RAT result within a day of the visit.

A chief manager of the authority, Gladys Kwan, said those visiting critically or terminally ill patients are allowed to use their negative RAT result to enter hospitals, but they must submit a PCR test result afterwards.

"For compassionate visits, the arrangement is still staying the same, because we try to allow flexibility for the family members to visit the patients when their condition is critical or [in a] dying situation," she said.

All visitors will also have to comply with the government's vaccine pass requirements.