Hundreds of patients who had treatment at an unregistered Melbourne beauty therapist may have been infected with hepatitis or HIV.

Hundreds of beauty patients could have caught hepatitis or HIV after visiting an unregistered Melbourne clinic where cockroaches were found crawling over dirty equipment.

More than 120 people received cosmetic services from a therapist at the Sonoun Kimlee Salon in the Springvale Shopping Centre, prompting the health department to call for them to immediately get blood tests.

The unregistered salon operated from the back of a jewellery shop from January 2018 until it was busted in May.

"This is one of the worst (cases) we have seen in terms of the practices and certainly one of the greatest risks for transmission of infection," Victoria's Chief Health Officer Brett Sutton told reporters on Wednesday.

"There appeared to be no evidence of cleaning and disinfection. There were cockroaches on medical equipment and it is pretty evident that the risk of infection was substantial."

Nearby workers alerted authorities to people leaving the clinic with bandages on their bloodied faces.

"We are concerned about the hygiene practices and therefore the potential transmission of hepatitis B, hepatitis C and HIV," Dr Sutton said.

The department has only been able to contact 68 people to date, with none yet tested for the diseases.

"But due to very poor record keeping, there are potentially a couple (of) hundred people or more who've been there," Dr Sutton said.

The salon offered tattooing, mole removal, facial fillers and skin cuts for skin tightening.

Dr Sutton said people could be permanently disfigured or blinded by untrained practitioners, and it was unclear if some equipment was used once, as intended, or multiple times.

The therapist, who only had basic cosmetic training, is a family member of the jewellery store owner.

Many of the clients are understood to have been members of Melbourne's Cambodian and Vietnamese communities.

The therapist worked alone, offered cheap prices, and it is believed she illegally imported Botox and fillers.

The woman has spoken with Dandenong council, who may prosecute the operator for breaches of the Public Health and Wellbeing Act.

There could be scope for police to lay other charges, Dr Sutton said.

The risk of Hepatitis B and C is considered moderate while the risk of HIV is low.

The Department of Health has set up a 1800 number for people who went to the salon to call if they have more questions.