An Adelaide paedophile who sexually violated more than a dozen children in Australia and Thailand, and shared videos of the abuse, has been described in court as one of Australia's worst child sex offenders.

Key points: Ruecha Tokputza abused at least 13 children from 2011 until 2018

Ruecha Tokputza abused at least 13 children from 2011 until 2018 He pleaded guilty to dozens of charges including indecent assault and indecent filming

He pleaded guilty to dozens of charges including indecent assault and indecent filming A prosecutor told the court his crimes were worse than those of Shannon McCoole

Over six-and-a-half years, Ruecha Tokputza sexually abused at least 13 children including one as young as 15 months old.

In some instances, the 31-year-old filmed and shared video of the abuse online.

Tokputza, who was born in Bangkok, performed various sexual acts on his victims, committing some of the crimes in Adelaide and others while he was in Thailand.

He pleaded guilty to 51 charges including aggravated indecent assault, sexual intercourse with a child under the age of 14 and engaging in sexual intercourse with a child outside Australia.

The Mile End man also admitted to indecent filming, as well as obtaining and producing child exploitation material outside Australia. One of the charges of sexual intercourse without consent was later withdrawn.

The offending occurred between June 2011 and his arrest in January 2018.

Tokputza was also found to have 12,500 images and 650 videos of child-exploitation material in his possession.

"It's hard to think of more serious offending," prosecutor Heath Barklay told the District Court.

"When you look at the constellation of charges, the persistent nature of the offending, the gross breaches of trust … the long duration of the offending … the very young age of the children, the number of victims — 13 at least identified."

Mr Barklay told the court Tokputza only stopped because he was caught.

He said Tokputza's offending was without comparison in Australian legal history and was "much more serious" than notorious Families SA paedophile Shannon McCoole.

McCoole was sentenced to 35 years in prison in 2015 for sexually abusing seven children and babies in state care.

"The offending in [the McCoole case] lasted about three-and-a-half years, he was sentenced on the basis that he had voluntarily assisted … had written an apology and … was remorseful for his offending," Mr Barklay said.

"In contrast to this matter, where there are 51 cases, 13 child victims, offending spanning six-and-a-bit years.

"In this case there is no remorse or no apology."

Lawyer pleads for leniency

The court also heard Tokputza had told a Swiss man he could "hook you up" if he travelled to Bangkok.

Tokputza is considered a serious repeat offender, the court was told, but a psychological report presented to the court stated: "There is prospect for rehabilitation."

His lawyer, Craig Caldicott, urged Judge Liesl Chapman to show leniency in sentencing.

"Simply, if we added up all the sentences we've got several life sentences," he said.

"It's not an easy matter but I would suggest that the sentence be fashioned in such a way that it does give him some hope of being released."

Judge Chapman will sentence Tokputza in May.