Nearly 100 cases have been detected in NSW since the start of June after just one case in the prior five months.

Another 110 cases of mpox have been detected in Victoria and 23 in Queensland since April.

The virus is transmitted chiefly through prolonged physical or intimate contact with an infected person.

A rash, lesions or sores, fever, chills, muscle aches, swollen lymph nodes and sore throat are among the common symptoms.

CSIRO virologist Nias Peng said the emergence was similar to the one in 2022, which he said saw the infection "neglected" in causing a global outbreak.

"The declaration of a public health emergency of international concern is timely to allow health authorities of respective nations to reinforce measures in order to curb the spread," he said.

"It is now time for us to act quickly to prevent history from being repeated."

Previously known as monkeypox, the disease is caused by infection with the mpox virus, which was first identified in monkeys.

The disease has made its way to Europe, with the deadly clade 1b variant detected in Sweden from a man who had travelled to Africa.

Many of central Africa's more than 15,000 cases are the deadly strain, which has not yet been detected in Australia.

NSW Health recommended sexually active gay and bisexual men (cis and trans) and their sexual partners, as well as sex workers and their sexual partners get mpox vaccinations and watch out for symptoms.

“People who have any symptoms of mpox - even if they have had the mpox vaccine and even if mild - should immediately contact their GP or sexual health service for an appointment," NSW Health executive director of health protection Jeremy McAnulty said.

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