An Australian mother has pleaded guilty to the manslaughter of her four-year-old son at the Brisbane Supreme Court on Wednesday (1 November).

Thirty-four-year-old Heidi Strbak appeared more than eight years after her son Tyrell Cobb was found dead in 2009 at their home on Gold Coast.

Strbak and her then-partner, Matthew Scown, 34, were initially charged with murder, but the charges were downgraded at a committal hearing last year.

According to reports, on 24 May 2009, Tyrell had begun vomiting after he was put to sleep by Strbak, who left the home to get cigarettes.

She left Scown to watch over the boy, ABC News reported.

Tyrell fell unconscious and Scown called 000 (the primary national emergency number in Australia) and started performed cardiopulmonary resuscitation on the boy as paramedics made their way to their home.

Tyrell was taken to hospital where he was pronounced dead. Police allege that the boy died from a blunt-force trauma injury to his abdomen and had sustained about 70 injuries over a period of time.

Scown walked from court last month after being sentenced to four years in jail for manslaughter. He has already spent two years and eight months in custody, 9 News website reported.

On his hearing, he had told the court that the boy was vomiting green matter on the night he died. The court was also told that Scown had punched or kicked the young boy in the stomach before his death.

"The contest will essentially be the allegation by the crown that she is in fact the author of the blunt force trauma which led to her son's death," Crown prosecutor Phil McCarthy was quoted as saying by ABC news website.

Strbak has been released on bail and will return to court on Tuesday (7 November) for a three-day contested sentence hearing.