A 12-year-old girl, sexually assaulted on her way to school on Monday morning, was able to give a "very clear" description of her attacker despite the ordeal, police say.

The girl was walking to school along a path at Narara, on the Central Coast, about 7.45am when she was grabbed from behind and dragged into nearby bushland.

Police have cordoned off a path where a schoolgirl was grabbed and sexually assaulted. Credit:Seven News

A man wearing camouflage clothing and wielding a hunting knife tied her up before she was sexually and indecently assaulted.

Police say the girl was eventually able to escape, running to school where she raised the alarm at 9am.