Health authorities on Saturday said two children infected with Covid-19 – including a 17-month-old toddler who received his first Sinovac jab on Friday – were in a serious condition and receiving intensive care.

The two cases were reported as Hong Kong recorded 8,457 new Covid-19 infections, including 232 imported cases, on Saturday. It was the second time this week that the daily case numbers were above the 8,000 mark.

Dr Lau Ka-hin, a chief manager at the Hospital Authority, said the 17-month-old boy was admitted to hospital on Friday as he had a fever and convulsions. He is suspected to have stopped breathing for a short period of time, before developing croup – a condition that leads to swelling of airways.

The toddler had received his first Sinovac jab on Friday, but Dr Lau said his symptoms had nothing to do with the vaccine.

"There was no documentation or history that the Covid vaccine can give rise to croup," Lau said. "And at the same time, the patient was found to have a viral infection of Covid... just a few hours after the Covid [vaccination]. So it is very likely that the patient got infected before the vaccination. The cause [of his symptoms] is the Covid-19 infection, it's not related to the vaccine.

"It is necessary to have Covid-19 vaccination earlier because it takes time for the vaccine to be effective after injection."

Another patient, aged 10, was in intensive care after doctors found shadows on both of his lungs. He had received two doses of vaccine.

Dr Lau noted that both boys now had stable vital signs after being treated.

A total of 2,387 Covid patients were being treated in public hospitals, including 12 who were in intensive care.

Four more Covid patients, aged between 69 and 91, have died.