A need to know more about the psychiatric issues of a teenager who raped a 17-year-old woman and an 11-year-old girl over a 24-hour period has delayed his sentencing for two months.

The 18-year-old Canterbury man, who has interim name suppression, has admitted two sexual assaults over the weekend of October 12 - 13 last year in Christchurch and North Canterbury.

He was due to be sentenced at Christchurch District Court today.

Judge Gary MacAskill adjourned it until April 30, calling for more psychiatric and psychological reports to be completed.

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The man, who has pleaded guilty to charges of kidnapping, threatening to kill, unlawful sexual connection, and rape, was remanded in custody until that date.

Crown prosecutor Sara Jamieson is asking for preventative detention to be considered, which means he would have to complete rehabilitation programmes and receive treatment to ensure he is no longer a risk to the public before he could be released.

Defence counsel Elizabeth Bulger provided the court today with a psychological report she had commissioned, which Judge MacAskill said he would read in chambers.

The court was earlier told that the terrified 11-year-old victim jumped from a speeding car fearing that the driver who had just raped her was going to kill her.

The older victim was raped in a car near Pound Rd, at the rear of Christchurch Airport on the night of October 12.

The pair, who police said were known to each other, met outside a bar before he restrained her in the passenger seat and attacked her.

She tried to fight him off, scratching his face, but he overpowered her.

The second attack came after the 11-year-old girl was abducted from a park's playground in rural North Canterbury, about 9.30am the next day.

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He drove her to a remote location, threatened her with a knife, and then sexually violated and raped her, a police summary of facts said.

The girl's father later saw them driving. He stopped his vehicle and stood in the middle of the road in an attempt to get the driver to stop, but he sped off.

The girl, fearing for her life, then managed to jump out of the speeding car.

She received scratches to her face and neck, grazes to her body, arms, and legs. She also had a cut to her thumb which happened while trying to evade a knife the teenager thrust at her.

The girl was later found by members of the public on a rural road.

Police spotted the man speeding in his car and after a pursuit, the offender's car hit a power pole in Loburn at about 150km/h, police say.

He was apprehended and treated in hospital before being taken into police custody.