A boy flown to Waikato Hospital in a serious condition after an alleged hit and run was described by family as having "tyre marks above his knees".

He suffered serious head injuries and abrasions to his limbs after being hit by a vehicle on Waingaro Rd in Ngaruawahia at about 1.30pm on Saturday.

An Auckland Rescue Helicopter Trust spokesman said the boy was a victim of an alleged hit and run accident.

A police spokeswoman confirmed the Serious Crash Unit was investigating but did not have any information to say the driver fled.

"Police were advised by ambulance of a collision between a car and a child. The child was responsive and airlifted to hospital by helicopter," the spokeswoman said.

The boy's mother said on social media the driver drove away from the scene and didn't return until well after her son was taken to hospital.

"My big son was watching him, they were crossing the road and the driver saw them and still hit my son."

Another family member said on social media the boy was having X-rays after a hard knock to his head.

"An onlooker said the van went straight over him which is terrible to think, he's so tiny. He has tyre marks above his knees and is just so sore right now."

In another incident, ARHT assisted a 60-year-old woman who was stung by a bee in the back of her head while walking near Whangapiro on Saturday morning.

"We were told she had walked about 100 metres when she started feeling dizzy and collapsed," the spokesman said.

He said the woman was flown to North Shore Hospital in a serious condition.