A collapsed bulk billing medical centre has been accused of systematically rorting Medicare over a number of years.

Tristar Medical Group collapsed in May this year, leaving hundreds of patients without access to medical services and owing creditors $23 million.

Leaked documents now suggest Tristar - Australia’s biggest bulk billing medical centre chain and mental health provider - rorted Medicare over a number of years, while authorities failed to act on tip-offs and red flags.

It is alleged that some Tristar GPs overstated the length of patient consultations to claim a higher Medicare rebate and billed for some services without adequate patient documentation, which is illegal.

Reports say some GPs charged Medicare for up to 18 hours of face-to-face patient consultations a day when the clinic was open for 10 hours. Individual doctors have been found to rake in almost $1 million, with nearly 90 per cent generated from Medicare billing.

The Tristar scandal has erupted during an inquiry into Medicare, which was launched last month by Health Minister Mark Butler in an attempt to quiet the growing calls for a royal commission into Medicare.

More details are accessible here.