The man aged in his 60s was sentenced in the County Court on Friday after he pleaded guilty to persistent sexual abuse of a child under 16, producing child "pornography", producing child abuse material, and knowingly possessing child abuse material.

The court heard the man sexually abused the young girl hundreds of times over a four-year period.

The man also took thousands of photos and videos of the girl for the purpose of creating child abuse material.

The man was caught after the United States Homeland Security department informed police that he was accessing child abuse material on an American website.

Police searched the man's home in April 2019 and located more than 2000 images and videos of the victim.

During his record of interview, the man told police he could not recall "all" of the offending against the victim and that he was "addicted" to child abuse material.

The victim's mother was alerted to the offending later that day and the girl was asked to give a statement to police.

The court heard the child could not complete the interview because she was "scared" she would be in trouble because the man had told her not to tell anyone.

Police searched the man's home a second time in July 2019 after the offender told a prison informant that there was more child abuse material.

Officers seized 12 USB devices, which showed about 150,000 child abuse images and videos.

The images depicted infants and children up to the age of 16. A significant portion of the material showed the man's victim.

Judge Paul Higham said the "depraved and perverted" offending would have had a "traumatic" impact on the young girl, who had her "innocence and childhood stolen".

The judge said the man had "reduced" his victim to the "state of a mere object" and his offending continued to escalate to an "ever-increasing depravity".

Judge Higham noted that the man had been long-term friends with the victim's mother and had been treated "like family" in the victim's home.

"It's almost trite to say it was a gross breach of trust," the judge said. "It was a fundamental betrayal."

Judge Higham said the man corrupted the young girl in a "purposeful, calculated, and relentless" fashion, and the man had "ample" opportunity to stop offending yet he continued.

The judge noted the man - who had been a bus driver at the time of the offences - was since diagnosed with paedophilic disorder.

Judge Higham said in sentencing, he would take into account the man's age, his early guilty plea, his significant health conditions, and his show of remorse.

But the judge said he needed to consider the protection of the community and general deterrence.

The man was jailed for 15 years and eight months, with a non-parole period of 11 years and two months. His 828 days in pre-sentence detention were reckoned as already served.

If he did not plead guilty, the man would have been jailed for 21 years and four months, with a non-parole period of 15 years and nine months.

The man will be on the sex offenders register for the rest of his life.

Affected by this story? There is help available.

You can phone the Centre Against Sexual Assault - Central Victoria on 5441 0430, or free-call the crisis care line 24 hours on 1800 806 292.

Or phone Lifeline on 13 11 14, the Blue Knot Foundation on 1300 657 380, or Relationships Australia on 1300 364 277.