Auckland, Sept 7 NZPA - A train driver saw a child's face looking up at him just before he struck a vehicle driven by a father accused of killing his four-year-old son in south Auckland, a jury was told today.

Alan Stephens, 40, pleaded not guilty to reckless driving causing manslaughter and three charges of reckless driving causing injury when he appeared in the High Court at Auckland.

The Crown alleges Stephens drove his car around barrier arms at the railway intersection at Paerata, near Pukekohe, in 2009, directly into the path of the train which slammed into the back of the car, killing his son Trae Blayde and injuring his daughters Shannyne, six, and Holly, two, and niece Nakita, 12.

Train driver Mark Leathart told the jury the car appeared in front of the freight train he was driving, after the driver ignored flashing lights and alarm bells at a railway crossing.

"I saw a child's face looking up at me just before I hit the car.

"I put the horn on straight away and applied the brakes in full service, which meant I could bring the train to a controlled stop," Mr Leathart said.

Crown prosecutor Kevin Glubb asked Mr Leathart if there was any way he could have avoided striking the car.

"It was instantaneous. One minute there was nothing there, and the next minute there was a car there. It was all so quick.

"The train was almost on top of the crossing. There was no way I would have seen the car in time," Mr Leathart added.

Mr Leathart has been driving trains for 28 years and was driving the Auckland to Wellington express freight train that day, the jury was told.

Quentin Duff, representing Stephens, chose not to cross-examine Mr Leathart.

Earlier today, truck driver Ioane Faalili told the jury that he was travelling along Karaka Road when he was overtaken by a silver Mitsubishi in the face of oncoming traffic.

"I was very shaken, I could see children in the car and I thought something might happen. I got my phone and took a photo of the vehicle.

"Two oncoming cars had to swerve off the road into the gravel."

As he approached the rail crossing Mr Faalili said he saw the train coming.

He heard the alarm bells ringing and the barrier arms were down but couldn't see the Mitsubishi.

I knew something had happened because the train had stopped.

"I went to have a look under the train and I saw the same silver car which had overtaken me earlier. I could not believe what I saw."

Trae sustained critical injuries and was flown by rescue helicopter to hospital, where he died later of his injuries. Nakita received severe head injuries and would have serious problems for the rest of her life, the Crown said.

Holly suffered subdural bleeding to the brain and Shannon received cuts and bruises, while Stephens was uninjured.

The Crown is expected to call 24 witnesses.

A jury of seven men and five women was sworn in yesterday for the trial set down for two weeks.

The jury was taken out to the scene yesterday afternoon.