Caleb Stroud came off his bike at 50kmh and slammed his head into a kerb. Thank goodness he was wearing a helmet.

A gift from a police officer has delighted a teenager laid up in hospital after crashing his bicycle.

Caleb Stroud suffered a brain bleed, a bruised lung and cuts and bruises after flying off his bike at 50kmh on Thursday afternoon.

Constable Pete Van't Wout, of Waikato's road police team, happened on the accident, stopped to help and then visited in him hospital bearing gifts, among them a new helmet.

REBEKAH PARSONS-KING/Fairfax NZ Caleb Stroud came off his bike in a busy street in Hamilton at high speed and hit his head on the kerb.

His old helmet probably saved his life, mum Karyn Stroud said, since he hurtled over the handlebars and hit his head on the kerb on River Road.

"The doctors said it could have been very different if his head had hit that kerb."

Caleb and younger brother Jesse had been heading home from Hamilton Boys' High School when the accident happened.

REBEKAH PARSONS-KING/Fairfax NZ Dad Andrew Stroud and Caleb with the new helmet and munted old one, which probably saved his life.

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As he went down the hill at the same speed as a car, his bike slipped out from under him at Tamihana Ave, Claudelands.

"His chain has come off and he has gone over the handlebars," his mother said from the surgical ward where Caleb is recovering.

"When Jesse got there, Caleb was unconscious and fitting."

Van't Wout came across the accident about 2.30pm and stopped to help.

"He continued fitting for some time when the policeman turned up and he's stayed with him," Stroud said.

Caleb was taken to Waikato Hospital by ambulance.

In an unexpected visit to the hospital on Friday morning, Stroud said Van't Wout had gone above the call of duty.

After liaising with Bike Barn in Hamilton, Van't Wout got Caleb a new helmet and free repairs to his bike.

"It is outstanding that he would come in and check up on my son, to stay with him at the time when he was off duty, and reassure him, try to keep him talking.

"And then to give him a helmet - I just think it is amazing, for me as a parent."

She said Caleb was initially shocked and then chuffed at the visit from the uniformed officer, who was finishing up his shift.

"It was so thoughtful, it's really amazing and he was touched he had come to see him."

In an update on Waikato's road policing page, Van't Wout shared his experience.

"I went to see the young boy at hospital at the end of my shift this morning. He was a little speechless as to what I was doing there. But once I got talking to him and gave him his new helmet, he was all smiles.

"He's doing well - no lasting injuries by the sounds of it - and he will be in hospital for the rest of the week and then continue some recovery at home."