The World Health Organization has said "sustained transmission" of monkeypox worldwide could see the virus begin to move into high-risk groups, like pregnant women, immunocompromised people and children.
WHO said this afternoon that it is investigating reports of infected children, including two cases in the UK, as well as following up reports in Spain and France.
None of the cases in children have been severe.
The virus has now been identified in more than 50 new countries outside the countries in Africa where it is endemic. Cases are also rising in those countries, said WHO, calling for testing to be ramped up.
"I'm concerned about sustained transmission because it would suggest that the virus [is] establishing itself and it could move into high-risk groups, including children, the immunocompromised and pregnant women," said WHO chief Tedros Adhanom Ghebreyesus.
The outbreak in newly-affected countries is primarily among men who have sex with men, and who have reported recent sex with new or multiple partners, according to the WHO.
People with symptoms are advised to avoid attending gatherings, while people in communities among whom monkeypox has been found to occur more frequently than in the general population should exercise particular caution, it says.
The normal initial symptoms of monkeypox include a high fever, swollen lymph nodes and a blistery chickenpox-like rash.
Meg Doherty, from the global HIV, hepatitis and sexually-transmitted infection programmes at WHO, said: "We are not calling this a sexually-transmitted infection.
"Stigmatising never helps in a disease outbreak," she added.
"This is not a gay disease. However, we want people to be aware of what the risks are."
