Italian and British medical experts investigate a possible connection between the coronavirus pandemic and severe inflammatory disease clusters among infants arriving in hospital with high fevers and swollen arteries.
Doctors in northern Italy, one of the hardest-hit areas in the world during the pandemic, reported extraordinarily large numbers of children under the age of 9 with severe cases of what appears to be Kawasaki disease, which is more common in parts of Asia.
"There are some kids who died who have had no underlying health conditions," Hancock told LBC Radio.
"It's a new disease that we think can be caused by coronavirus and COVID-19 virus, we're not 100% sure because some of the people who got it hadn't tested positive, so we're doing a lot of research now, but it's something we're worried about." Up until now, children were thought to be much less susceptible than their parents or grandparents to the most deadly complications they've had.
"It's rare, though it's very significant for those kids who do get it, the number of cases is small," said Hancock, one of the ministers leading the response from Britain to COVID-19.
He hasn't given the exact number of deaths.
Kawasaki disease, the cause of which is not known, is associated with fever, skin rashes, gland swelling and, in severe cases, heart artery inflammation.
According to the United Kingdom National Health Service, the syndrome affects only about eight out of every 100,000 children a year, with most under 5 years of age.
There is some evidence that individuals may inherit a disease predisposition but the pattern is unclear.
Children who have either tested positive for COVID-19 or for their antibodies have had gastrointestinal symptoms such as abdominal pain, vomiting, and diarrhea over the past two weeks, the Spanish Pediatric Association said Monday.
Though the kids were otherwise in good health, their condition could develop into shock within hours, with tachycardia and hypotension even without fever.
The majority of cases were detected in minors of school age or adolescence, and sometimes overlapped with Kawasaki disease or toxic shock syndrome (TSS).
Junior British interior minister Victoria Atkins said parents should be vigilant.
"It shows just how fast this virus is moving and its effect is unprecedented," Atkins told Sky News.
The president of the Royal College of Nursing, Professor Anne Marie Rafferty, said she had heard reports about the similarity of cases in infants with Kawasaki syndrome.
"There's far too little actually known about it and the numbers are really too small at the moment," Sky News said. "But it's an alert, and it is something that a number of different researchers are actually exploring and examining."