Emergency services were called to the Castlereagh Highway at Merrygoen, about 10km east of Mendooran, at 3.20pm after a 2005-model Mitsubishi 380 sedan travelling west left the road and hit a tree.

The driver and four passengers were trapped in the vehicle and had to be released by emergency services.

The front-seat passenger, a 14-year-old boy, and a 25-year-old man, who was in the back seat, died at the scene.

Three other people were seriously injured.

The driver, a 37-year-old woman, was airlifted to Westmead Hospital with arm fractures.

A 13-year-old boy was airlifted to The Children's Hospital at Westmead with multiple leg injuries, and a 17-year-old girl was airlifted to John Hunter Hospital also suffering leg fractures.

The 25-year-old man was from Gulgong, while the others are all from Menah.

Officers from the Crash Investigation Unit are investigating the circumstances surrounding the crash.

Anyone with information about this incident is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au. Information is treated in strict confidence.

The public is reminded not to report crime via NSW Police social media pages.