The World Health Organisation says monkeypox constitutes a moderate risk to overall public health at global level after cases were reported in countries where the disease is not typically found.

"The public health risk could become high if this virus exploits the opportunity to establish itself as a human pathogen and spreads to groups at higher risk of severe disease such as young children and immunosuppressed persons," WHO said.

WHO said the sudden appearance of monkeypox at once in several non-endemic countries suggested undetected transmission for some time and recent amplifying events.

As of May 26, a total of 257 confirmed cases and 120 suspected cases had been reported from 23 member states that were not endemic for the virus, the health agency said on Sunday.

There has been no reported fatalities.

The agency said it expected more cases to be reported as surveillance in endemic and non-endemic countries expands.

Monkeypox is an infectious disease that is usually mild, and is endemic in parts of west and central Africa. It is spread by close contact, so it can be relatively easily contained through measures such as self-isolation and hygiene.

Most of the cases reported have been detected in the UK, Spain and Portugal.

"The vast majority of reported cases so far have no established travel links to an endemic area and have presented through primary care or sexual health services," the UN agency said.