NSW Health says nine of the infections were probably acquired overseas but two may be local cases, which suggests community transmission could be occurring, especially among men who have sex with men.

"People need to be aware of the symptoms of monkeypox, which can include fever, headache, body aches and a rash or lesions on the genital area," NSW Health executive director of health protection Jeremy McAnulty said on Wednesday.

He said the cases had not exhibited severe symptoms, such as an extensive rash or lesions all over the body.

But Dr McAnulty warned even minor symptoms such as pimples in the genital area or buttocks needed to be taken seriously.

"The virus is mainly spread through skin to skin contact ... It is important that people with symptoms avoid close contact with others, including sexual activity."

Monkeypox is a rare viral infection associated with travel to Central and West Africa.

However, thousands of cases of monkeypox have been reported in Europe and the United States.

The disease can be transmitted through air droplets, close contact and sharing contaminated linen or objects.

Many of the cases have been among men who have sex with men.

Australian Associated Press