The mother of two teens killed in a Christmas Day car crash has gone on trial this morning for her alleged part in a "reckless" road race that ended in their deaths.

Merepeka Morehu-Clark, 14, and her sister Brooklyn Morehu-Clark, 13, were killed in Tauranga on Christmas Day 2011 after the car they were in collided with a utility on Welcome Bay Rd.

This morning in the High Court in Hamilton Phillippa Vanessa Morehu, 37, and the girls' cousins Hetaraka Hikurangi Reihana, 21, and Haki Tepuere Davey, 18, pleaded not guilty to two charges each of manslaughter, caused by dangerous driving.

Reihana was alleged to have been driving the car in which the sisters were back-seat passengers.

Crown prosecutor Greg Hollister-Jones told the jury that Reihana was drunk and unlicensed when he went to overtake Morehu's and Davey's cars in a high speed race involving unsafe cars.

As he was overtaking he crashed head-on into a ute coming in the opposite direction.

Hollister-Jones said the force of the crash was such that the ute did a complete tail-over-nose and landed on its roof.

Miraculously the driver escaped relatively unscathed, but the two sisters - who were not wearing seatbelts - were thrown from Reihana's vehicle and killed instantly.

Also in Reihana's car was his mother and his two-year-old daughter, who were sitting in the front.

Hollister-Jones described the defendants actions on the day as "reckless and criminal" and said Morehu and Davey were just as liable as Reihana, even though they didn't crash.

He said "alcohol-fuelled madness" led to the death of the two young sisters that day.

The trial is set down for three weeks in front of Justice Murray Gilbert and a jury of two men and 10 women.

- © Fairfax NZ News