A Victorian man has become the fifth monkeypox case detected in Australia after returning from the United Kingdom.

The returned overseas traveller, aged in his 30s, developed mild symptoms after arriving back in Melbourne and seeking medical attention.

Testing has confirmed he has the virus and is isolating at home. It is the second confirmed monkeypox case in Victoria and the two infections are unrelated.

A small number of the man's contacts have been contacted by the health department and told to monitor for symptoms.

Monkeypox can be transmitted from person to person through air droplets, close bodily contact or sharing contaminated linens or objects.

Symptoms include fever, headache, muscle aches and exhaustion.

Victorian Chief Health Officer Brett Sutton said the viral disease is not easily spread and usually resolves on its own within two to three weeks.

"Monkeypox isn't easily transmitted from person to person, as it requires direct skin to skin contact through broken skin, fluid or pus in lesions, or prolonged face to face contact via respiratory transmission," he said.

It comes after a NSW confirmed its third monkeypox case, a man in his 50s who also recently returned from Europe.

The man developed a mild illness several days after arriving back in Sydney, NSW Health said on Friday.

He is isolating at home and his case is not connected to two previous cases detected in NSW.

NSW Chief Health Officer Kerry Chant similarly sought to temper worries about the spread of the disease.

"Monkeypox does not present a transmission risk to the general community, and has until recently not been an infection most clinicians in NSW would have been looking for or concerned about in their patients," she said.

The World Health Organisation said 23 countries that are not endemic for monkeypox virus have reported cases since mid-May.

Community health charity ACON has advised men who have sex with men to be vigilant for symptoms.