Police are investigating the death of a teenager at Charlestown overnight, which is being treated as suspicious.

Officers were called to a unit on Charlestown Road at Charlestown around 12.30am on Tuesday morning following reports a 16-year-old was found unresponsive.

When they arrived, the boy was found deceased inside.

Officers attached to Lake Macquarie Police District established a crime scene and commenced an investigation into the circumstances surrounding the teen’s death.

Following inquiries, a 24-year-old man was arrested in a restaurant carpark on Weakleys Drive at Thornton around 2.10am.

He was taken to Maitland Police Station before being transferred to the Mater Hospital for treatment.

Upon his release, he was taken to Belmont Police Station where he is currently assisting police with their inquiries.

Investigations are ongoing.

The pair are known to each other.