A man has been charged with sexually assaulting a teenage girl after picking her up as she hitchhiked on the New South Wales mid-north coast.

Police say the 43-year-old picked up the 15-year-old in the Coffs Harbour area last week and drove her to his house.

The girl has told police the man, who she did not know, then gave her marijuana and sexually assaulted her.

Detectives from the Child Abuse Squad squad arrested the man yesterday and charged him with aggravated sexual assault, two counts of indecent assault and two counts of possessing a prohibited drug.

He was held in custody overnight to face Coffs Harbour Local Court today.