More than 550 confirmed cases of monkeypox have now been reported to the World Health Organization (WHO) from 30 countries that are not endemic to the monkeypox virus, WHO chief Tedros Adhanom Ghebreyesus told a briefing on Wednesday.

He said the sudden appearance of monkeypox in several countries around the world suggests the virus has been spreading undetected for some time outside western and central Africa.

Rosamund Lewis, WHO's monkeypox technical lead, said WHO has no answers about the source of the outbreak, according to CNN.

"We don't really know whether it's too late to contain. What WHO and all member states are trying to do is prevent onward spread," Lewis said at a news conference in Geneva on Wednesday.

According to WHO, most people recover from the disease within several weeks without requiring hospitalization. Vaccines against smallpox, a related disease, are also effective in preventing monkeypox and some antiviral drugs are being developed.

However, WHO also warned "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."

Currently WHO urges countries and health organizations to closely monitor the virus spread and provide testing to anyone who has symptoms such as rash, fever, swollen lymph nodes, headache, back pain, muscle aches and fatigue.

"We are not concerned [about] a global pandemic" from monkeypox at the moment, Lewis said at a news briefing on Monday.