Police map the scene on Von Tempsky St where incident happened.

A schoolboy has been hit by a truck during rush hour in central Hamilton.

The incident happened on Von Tempsky St, near the Anzac Parade bridge in Hamilton East about 8am.

Witness Broc Ganz was on his way to work in the central city on Thursday when he saw the boy underneath a truck.

JO-LINES MACKENZIE/ STUFF The truck at the intersection in central Hamilton.

Two police cars had blocked off the Von Tempsky St entrance and traffic was backed up, he said.

"There was a medium-sized truck with gas cylinders on the back, and all I could see was that a kid was underneath with what looked like a bike."

He said a group of other children on bikes were watching and waiting on the footpath.

"He wasn't under the wheel or anything, but he was underneath, trapped in the middle on his side."

Sergeant Todd Hubbard, speaking at the scene, confirmed the schoolboy was knocked off his bike by a truck carrying gas cylinders.

The boy was conscious and talking after the incident and Hubbard said police would speak with him later.

He was taken to Waikato Hospital in a serious condition at 8.10am on Thursday, a St John spokesperson said.