The father of an 11-year-old boy who survived a night alone in the bush in freezing temperatures in Sydney’s northwest has been arrested on unrelated drug charges.

Christopher Wilson’s father was arrested on Thursday after a hydroponic cannabis lab was found, police confirmed to AAP on Thursday.

The boy went missing after getting off the school bus on Wednesday afternoon at Annangrove.

Superintendent Darrin Batchelor said the family was “extremely relieved” after enduring more than 16 hours “distraught with worry” about the boy, who was wearing shorts, a t-shirt, a light jacket and had no food or cash.

The alarm was raised when the quiet youngster failed to return home and an extensive search was launched overnight involving police PolAir, the SES and RFS.

Fears for his safety mounted when no trace of the boy was found and the overnight temperature dipped as low as three degrees, with the wind chill factor making conditions “absolutely freezing”.

Supt Batchelor said Christopher was spotted by a woman driving on Annangrove Road, not far from his home on Thursday morning.

“He was quite cold obviously … she gave him some water and a muesli bar and he was quite happy to be in a bit of warmth and get something to eat and drink,” he said.

The boy was checked by paramedics and had no visible injuries but had been taken to hospital with possible mild hypothermia to be reunited with his parents.

“They were distraught with worry overnight and yesterday afternoon so it’s a great outcome,” Supt Batchelor said.

The boy was very cold and not inclined to share what happened to him with police officers, but they believe he slept somewhere in the bush overnight.

“We haven’t filled in all the pieces of the puzzle yet, but it looks like Christopher went on a little bit of an adventure yesterday afternoon,” he said.

“At this stage it doesn’t look like anyone else was involved.”