Good Samaritan and cop 'attacked' in NSW

A good Samaritan and a police officer have allegedly been attacked after trying to come to a woman's aid in NSW.

The witness, aged 28, tried to intervene after seeing a man assault his female passenger inside a parked car at Newcastle around 12.35am on Sunday, it will be alleged.

The couple - a 29-year-old man and 32-year-old woman - then turned on the man and allegedly assaulted him.

Police were called and found the pair with a third man, aged 20, nearby.

The 20-year-old is accused of punching an officer in the head several times before the trio resisted arrest.

The older man remains under police guard in hospital and is expected to face charges, with the other two set to front court to answer a raft of charges.