An 18-year-old youth has admitted having sex with two underage girls after Facebook hook-ups, and supplying one of them with cannabis.

Vaughn Danile-Roy Coxhill, unemployed, pleaded guilty to these charges as well as meeting one of the girls for sex after "grooming" through the website and text messaging.

The girls were aged 14 and 15.

Police said Coxhill met the first girl through Facebook, where she gave her age as 14.

He gained her confidence through their online and text conversations and discussed meeting her for sex.

On April 21, he took her to his mother's house where they had sex in a bed set up in the kitchen.

He had heard of the second girl, 15, through associates and when he was in Bromley Cemetery with friends he asked one of them to invite her to join them for some cannabis.

Coxhill then contacted the girl through Facebook and met her several times.

He met her at the New Brighton Library on May 3, and he later took her to an associate's house where he bought cannabis and shared it with her.

They then spent the night at his mother's house and had sex.

When police interviewed Coxhill, he said he knew it was wrong, but the first girl had "asked me to do it".

Coxhill's first strike warning will be given at sentencing under the Government's tougher sentencing regime for repeat violent offenders.

Christchurch District Court Judge Phillip Moran remanded him in custody for a Crown sentencing on October 11. A pre-sentence report will consider his suitability for home detention.

Defence counsel Mark Callaghan said there was no address for him to stay at while on bail, and the judge said an application could be made if an address became available.

- © Fairfax NZ News