A boyracer who drove over a passenger ejected from another car after a horror 150km/h street race crash fled the scene, fearing he had "just killed someone".

William James Henry Le Grys, 20, was driving a Honda through Christchurch at about 8.30pm on July 2 this year when he started tailgating a Holden, "enticing" the other driver to race.

The Holden driver obliged and a race began along the two-lane Russley Rd.

Le Grys reached speeds in excess of 150km/h, police say.

Advertisement

When he caught innocent motorists, he began weaving between them, constantly changing lanes to pass them, Christchurch District Court heard today.

During the "weaving manoeuvres", the Holden driver lost control and went into a tail spin.

He smashed into a concrete culvert and his passenger - and brother - was ejected out of the car.

Le Grys, who was travelling close behind, was unable to avoid him and drove over top of him.

He then fled the crash scene without checking on the victim, later telling police he "panicked thinking he had just killed someone".

The victim suffered "quite horrific injuries", police said today, including an unstable fractured pelvis, a fractured left collarbone, and punctured lungs.

He spent "several days" at Christchurch Hospital, a police summary of facts states.

Today, Le Grys pleaded guilty to charges of being party to operating a motor vehicle in a race causing injury and failing to stop and ascertain injury after a crash.

The police summary of facts says he is""extremely remorseful".

Judge John Strettell remanded him on bail until October 19 for a restorative justice meeting to be considered.