Police are hunting a man who approached a young girl with a hammer at a Waikato school.

He reportedly jumped a fence at Te Pahu School, a rural school about 30km south east of Hamilton yesterday.

Senior Sergeant Robbie Hermann told Fairfax the school went in to lockdown about midday.

He was described as bald with a goatee, "scruffy looking" and aged in his 30s-40s.

​Police said they had an idea of who the man might be.

A local told the publication: "He parked his car right next to our school field jumped the wooden fence. He was carrying a hammer. He ran up to girl who was playing, she ran away as fast as she could and got away.

"He returned to his car, stood by his car for a while staring at the kids, then he put the hammer in his boot, got back in his car and drove off."

She said teachers reacted quickly, placing the school in lockdown.

"But when is too late too late? We have a pre-school up the road with kids freely playing by the fence line. I'm terrified."

-NZ Herald