NHS doctors have been issued an urgent alert about a sharp rise in the number of children being admitted to intensive care with a coronavirus-related condition.

In an alert sent to GPs, health chiefs said: ‘There is growing concern that a [COVID-19] related inflammatory syndrome is emerging in children in the UK.

‘Over the last three weeks there has been an apparent rise in the number of children of all ages presenting with a multi-system inflammatory state requiring intensive care across London and also in other regions of the UK.’

Children are not thought to be badly affected by COVID-19 – very few have been diagnosed around the world since the pandemic began and even fewer have died.

Young people’s apparent resilience to the disease has baffled doctors for weeks because they are often ‘super-spreaders’ of viral illnesses such as flu.

The children being seen with this condition are commonly suffering from stomach pain and ‘gastrointestinal symptoms’ – which could include vomiting and diarrhoea.

Doctors have compared the mysterious condition to toxic shock syndrome and Kawasaki disease which, combined, cause harmful internal swelling, fever and breathing problems – all hallmark signs of COVID-19.

But some of the children presenting with the illness have tested negative for the coronavirus, further complicating the diagnosis.

It is not clear how many children have been diagnosed with the illness, nor whether any have died with it, but it is thought to have only affected a small number of patients so far, the Health Service Journal reported.

The memo, which was sent out by an NHS trust in London and tweeted by the Paediatric Intensive Care Society, said: ‘The cases have in common overlapping features of toxic shock syndrome and atypical Kawasaki disease with blood parameters consistent with severe COVID-19 in children.’

The alert told GPs to refer children with symptoms including abdominal pain as a ‘matter of urgency’.

If the condition turns out to be more widespread it could add a new element of danger to the coronavirus outbreak, which so far appears to be sparing children.

Only nine people under the age of 19 have died in England with COVID-19, out of a total of 18,420 reported by yesterday, April 26 – 0.05 per cent.

The reasons for this are unclear but scientists have suggested that lower rates of other serious illnesses and a lack of age-related lung damage may be protective.

According to the NHS memo, cases of this inflammatory syndrome have only started to appear in the past three weeks – this may be because it is slow to develop or so rare that it has only become noticeable in the peak of the UK’s epidemic, when around a million people are believed to have been infected in London alone.

A paediatrician at St Mary’s Hospital in the capital, Dr Elizabeth Whittaker, said on Twitter that medics in other countries had reported the same illness.

Dr Whittaker said: ‘Our Italian and Spanish colleagues also report it. Numbers are small but significant. We want primary care /A&E to be vigilant so those affected are in the right place to get appropriate supportive care if needed.’

MailOnline has approached NHS England and the Royal College of Paediatrics and Child Health for comment.