South Auckland Police are investigating the sexual assault of a 14-year-old-girl in Papakura.

The girl entered Kirks Bush via a walkway from Rosehill Drive around 4pm yesterday.

She was grabbed from behind by an unknown man with a grey t-shirt over his face and thrown to the ground.

After a struggle the victim managed to break free and the offender ran off.

The man's described as about 20-years-old, Maori, 167 centimetres tall and has a Maori design tattoo on his left arm.