Adelaide man's sex crimes are the worst of their kind in Australian legal history, court hears.

The crimes of an Adelaide child sex tourist are the most serious of their kind in Australian legal history, a court has heard.

Ruecha Tokputza, 31, appeared in the District Court on Wednesday after pleading guilty to 51 charges against 13 babies and boys over more than six years.

He groomed Australian and Thai children for sex, filmed their abuse and shared it online.

Prosecutor Heath Barklay SC told the court there was “no body of comparable cases” for Tokputza’s crimes because of the multi-faceted way in which he offended.

Mr Barklay said his actions were more serious than those of notorious Families SA pedophile Shannon McCoole, who was sentenced to 35 years in jail in 2015.

He said a major difference between the pair was McCoole’s remorse, which he showed through a letter of apology to his victims.

“When one contrasts the two in that way, in my submission, this matter is plainly much more serious,” Mr Barklay said.

“It’s for that reason that there is a limit to the use of the McCoole matter in this case.”

McCoole also committed fewer crimes – 20 offences against seven victims over the span of more than three years.

Craig Caldicott, for Tokputza, asked Judge Liesl Chapman to hand his client a sentence that could have him released on parole after he had undergone rehabilitation.

“I would suggest that the sentence should be fashioned in such a way that it does give him some hope of eventually being released,” he said.

Tokputza was arrested following a joint investigation by Australian Federal Police, SA Police, NSW Police and Interpol.

His charges include sexual intercourse with a person under 14, aggravated assault, engaging in sexual activity with a child outside Australia and transmitting child exploitation material.

Judge Chapman will sentence Tokputza in May.