A paediatric specialist has called on parents to keep a close eye on their children who are infected with Covid, saying hospitals are seeing more croup cases as well as a post-Covid condition that could put them into an intensive care unit.

Children who have croup may suffer from breathing difficulties and make a noisy, high-pitched sound as the condition leads to swelling that narrows their airways.

Dr Mike Kwan, a consultant in the Paediatric Infectious Diseases Unit of Princess Margaret Hospital, said they are now seeing a new croup case every day or two.

He also urged parents to be vigilant even after their children recover from Covid-19, saying they may suffer from an after effect that could require critical care in hospital.

Kwan said nearly 60 children had been diagnosed with Multisystem Inflammatory Syndrome (MIS-C) two to eight weeks after they had been confirmed to have Covid.

He said symptoms of MIS-C patients include high fever, skin rash, pink eye and a swollen and bumpy tongue - known as strawberry tongue.

Kwan said MIS-C could affect the patient's heart, brain, liver and kidneys.

"This condition is actually quite serious and can be life-threatening. And in Hong Kong around half the children needed to be admitted to the paediatric intensive care unit, and treated with high-dose steroid and also intravenous immunoglobulin," he said.

Fortunately, all children who had MIS-C were recovering nicely, the specialist added, although the Hospital Authority would offer follow-up services to see whether the illness would cause any long-term complications.

"This condition warrants long-term follow up, and we are planning to follow up on these children in the Hong Kong Children's Hospital."

Kwan appealed to parents to get their children vaccinated against Covid, saying most of those who've developed MIS-C had not had jabs.

He also revealed that a girl previously infected with the coronavirus has been suffering from brief loss of vision once or twice a day.

"This is a temporary visual loss that happens around 10 to 30 seconds each time, which quite affects her daily life. Now we are working with multiple specialists to try to help this girl," he said.

While doctors have yet to establish the cause of her vision problem, the specialist suspects it could be that the coronavirus has affected her central nervous system.

The girl, he said, is one of the 288 children he's seeing who were previously infected with Covid.

Kwan said a fifth of them had developed at least one long-term symptom of the virus, like headaches, hives or serious hair loss.