A Colombian teenage skateboarder has pleaded guilty to a series of horrific sex attacks on women in Melbourne's CBD.

Prosecutor Dr Nanette Rogers, SC, told the County Court the teenager was 17 years old when he randomly attacked three women on three separate occasions over a three-month period from November 2013 to January this year.

Ms Rogers said the teenager had choked each of his victims until they lost consciousness before he sexually assaulted them during the brazen and predatory attacks.

The teenager's first victim was a 22-year-old woman who was walking along Bourke Street about 12.30am on November 9 when she was grabbed and forced into a laneway before being attacked.

The second victim was a 24-year-old woman who had been sitting on a fence talking on her mobile phone outside a car dealership on Kings Way, near Albert Road, when the teenager grabbed her from behind between 2.30am and 3am on December 7 and sexually assaulted her.

The third victim was a 22-year-old woman who was grabbed in a headlock by the teenager as she was walking in Flinders Lane about 6am on January 18.

Ms Rogers said the teenager put a shard of glass to the terrified woman's neck and forced her to walk with him through the city for more than a kilometre before he raped her twice in a stairway near the Southern Cross railway station.

The teenager was arrested on January 24 at a camping ground in Johanna, near Apollo Bay.

The teenager, who turned 18 in August, pleaded guilty to a number of charges including rape, attempted rape, robbery, assault with intent to rape and indecent assault.

The prosecutor said the Children's Court had decided to send the case to the County Court because the offences were so serious. If the teenager had been sentenced in the Children's Court, the maximum sentence he could have received was three years' jail.

The prosecutor said the teenager's parents had helped him to change his appearance and had booked him a one-way flight back to Bogota, Colombia, which had been due to fly out the day after his arrest.

In a victim impact statement read to the court, the second victim, a Chinese international student, said her parents had picked out Australia as the place for her to study because it had a reputation for good public security and no discrimination.

"Sexual abuse is an unforgivable offence," the student said. "It should not have happened here [in Australia]."

The third victim said she was constantly flooded with painful memories of the day she was raped by the teenager.

She had been unable to tell her family what had happened because she was worried they would feel as devastated about the horrific crime in the same way she had been devastated.

The woman described how she had had to endure an excruciating 12-week wait for the results of blood tests to see if she had contracted HIV.

Her feelings of love and connection with others had been diminished by the crime.

She no longer went to the gym because she had a creeping thought that if she made herself as unappealing as possible, she would be less vulnerable to being attacked again.

The court was told the teenager, who emigrated to Australia early last year to be with his mother, was sorry for what he had done but blamed alcohol abuse for the last two attacks.

The teenager will be sentenced at a later date and is expected to be deported when released on parole.