Authorities in Australia have issued a warning to patients of a retired dentist, urging them to test themselves for bloodborne viruses due to "poor infection control practices" at the clinic.

Thousands of patients at Dr William Tam's clinic in Strathfield, western Sydney may have been exposed to hepatitis B, hepatitis C and HIV, the New South Wales state health ministry said in a statement on Wednesday.

The Ministry urged patients to see a doctor and test for such viruses, thought it noted that the "risk is low".

Tam is now retired and de-registered as a dentist, the statement said.

"The poor infection control practices at Dr Tam's practice means all former patients may be at low risk of a blood borne virus infection, which can have serious and long-lasting health impacts," Dr Leena Gupta, the public health clinical director of the Sydney Local Health District, said in the ministry statement.