The UK Health Security Agency is investigating 74 cases of hepatitis among children across the UK.
The health body is examining 49 cases in England, 13 in Scotland and 12 across both Wales and Northern Ireland, all of which have occurred since January.
The UKHSA said that it is investigating a “number” of possible causes of the cases.
One potential line of inquiry is whether or not a group of viruses called adenoviruses may be causing the illnesses.
Other possible explanations are also being investigated, including whether or not Covid-19 could have played a role in the spate of cases.
But officials stressed that there is “no link” to Covid-19 jabs as none of the children affected have received a Covid-19 vaccine.
Dr Meera Chand, director of clinical and emerging infections at the UKHSA, urged parents to be alert to the signs of hepatitis amid the rise in cases.
She said in a statement: “We are working swiftly with the NHS and public health colleagues in Scotland, Wales and Northern Ireland to investigate a wide range of possible factors which may be causing children to be admitted to hospital with liver inflammation known as hepatitis.
“One of the possible causes that we are investigating is that this is linked to adenovirus infection.
“However, we are thoroughly investigating other potential causes,” she added.
“Normal hygiene measures such as good handwashing, including supervising children, and respiratory hygiene, help to reduce the spread of many of the infections that we are investigating.
“We are also calling on parents and guardians, to be alert to the signs of hepatitis, including jaundice, and to contact a healthcare professional if they are concerned.”