Reports of a possible link between coronavirus and an inflammatory syndrome affecting young children are now coming from the United Kingdom, United States and Italy.

In the UK, health authorities say as many as 12 children, some of whom have tested positive to COVID-19, are seriously ill in hospital with high fevers and swollen arteries.

It prompted Britain's National Health Service to issue an alert to doctors that the condition could be related to coronavirus in children.

In the US, a doctor from Columbia University Medical Center in New York said three children infected with coronavirus were being treated for an inflammatory syndrome that appeared similar to Kawasaki disease.

Meanwhile, doctors in northern Italy, where COVID-19 has been rampant, have also reported children under the age of 10 being affected by what appeared to be the inflammatory condition.

But as very few cases have appeared worldwide, and Kawasaki disease is considered extremely rare and mostly recoverable, Australian experts are urging parents to remain calm.

What is Kawasaki disease?

Kawasaki disease is a rare but potentially severe inflammatory condition in children, most common in those under five years old.

It is a form of vasculitis, which means it causes the walls of blood vessels in the body to become inflamed.

It was first reported by Japanese paediatrician Tomisaku Kawasaki in the 1960s.

Most children recover completely from Kawasaki disease after a few weeks, but early treatment is necessary to prevent possible complications.

In severe cases, if left untreated, the disease can lead to damage to the coronary arteries. In the absolute worst cases that can lead to a heart attack or impact the likelihood of one later in life.

Doctors say it's too early to draw a definitive link between coronavirus and the childhood inflammatory syndrome. ( ABC News: Brant Cumming )

The cause of Kawasaki disease is unknown, though it is believed to be triggered in response to an infection.

Because the cause is not known, there is also no prevention for Kawasaki disease, though treatment — an intravenous drip of immunoglobulin (or antibodies) — is highly successful.

What are the symptoms?

Children with Kawasaki disease most commonly have:

a high fever that lasts several days

a high fever that lasts several days a rash

a rash bloodshot eyes

bloodshot eyes red or cracked lips

red or cracked lips joint pain

joint pain swollen hands and feet

They may also have symptoms that appear similar to sepsis — a condition caused by the immune system's response to an infection — such as being drowsy or lethargic and having difficulty breathing.

In the cases of the children in the UK, US and Italy showing some symptoms of Kawasaki disease and sparking concern about a possible link to COVID-19, they have also shown signs of toxic shock syndrome or gastrointestinal issues, including abdominal pain, vomiting and diarrhoea.

Is there a link between Kawasaki disease and coronavirus?

No, not officially.

In its alert to doctors, the British National Health Service said it had seen a higher-than-normal number of children presenting with an inflammatory syndrome, some of whom had also tested positive to COVID-19.

It speculated there could be a link, but also said there "may be another as-yet-unidentified infectious pathogen associated with these cases".

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Either way, the alert was sent to doctors so they could monitor any emerging cases and provide the correct treatment to children as quickly as possible.

What do Australian experts say?

"If there's a link, it's a rare link," Professor Robert Booy, an expert in child health and Kawasaki disease from the University of Sydney, said.

"Most children who have COVID-19 have mild symptoms or no symptoms and mostly they are respiratory, not inflammatory.

"Though, it's certainly possible there is a connection because it is a combination of rare diseases."

Dr Booy, who was previously a professor of paediatrics at the Royal London Hospital where he ran a study on Kawasaki disease, said COVID-19 could be acting as the "unknown infection" that (in rare cases) could lead to the inflammatory syndrome.

Or, he said, as coronavirus damaged the digestive tract, it could allow bacteria to invade and cause secondary trouble.

Leading Australian paediatric infectious diseases expert David Burgner, from Murdoch Children's Research Institute, agrees that it's possible.

"There are increasing reports that the illness we are seeing in adults, the sudden deterioration after one week, is due to changes in the blood vessels rather than changes in the lung," Dr Burgner said.

"The changes we are hearing about from the UK, which are typical of Kawasaki disease and toxic shock, those are illnesses that predominantly affect the blood vessels.

"That's in keeping with our evolving understanding of what COVID-19 can do."

But both doctors said it was far too early to draw a definitive link between the childhood Kawasaki disease and coronavirus, given the incredibly small number of possible patients worldwide.

Is my child at risk?

Australian parents should be "not at all worried" that their children could attract a severe inflammatory disease as a result of coronavirus, Dr Booy said.

He was quick to reiterate that COVID-19 appeared to affect a very small number of children.

So far during the global pandemic, few children worldwide have contracted coronavirus, and fewer still have become very sick.

"Inflammatory syndromes are rare as a complication anyway, but we also have so few cases of COVID-19 in Australia that I don't expect to see an increase in Kawasaki disease here," Dr Booy said.

Dr Booy says while we don't know why children are less affected by coronavirus than adults, it is not without precedence.

"This is a weird virus and it's very damaging to adults and elderly, but somehow children and teenagers are minimally affected," he said.

"Though it's not as if we haven't seen this before. There is also evidence with previous epidemics, such as the influenza pandemic known as the Spanish flu, that children have been spared."

Dr Burgner says in Australia, where the number of people infected with COVID-19 continues to fall, parents shouldn't be overly worried.

"These are rare conditions so the risk to an individual child is low, so we can be reassuring about that," he said.