TWO people have been killed in one day in separate crashes on NSW roads.

In the first accident, on Sydney's Northern Beaches, a female front-seat passenger in a Nissan Skyline car died after the vehicle left the road and hit a power pole.

The woman, thought to be in her 20s or 30s, died at the scene of the crash on Myoora Road at Terrey Hills, which happened at 6am (AEST) today.

The driver, a 33-year-old man from the Northern Beaches, was seriously injured. He was airlifted to the Royal North Shore Hospital in a critical condition.

A 30-year-old man from Cabramatta, who was in the back seat, was airlifted to Westmead Hospital in a serious but stable condition.

The second crash happened on the Hume Highway, 7km south of Holbrook, at about 5pm when a Toyota Corolla left the highway and hit a tree.

A man in the front passenger seat died at the scene, while the driver and three other passengers were taken to Albury Base Hospital.

The driver and two of the passengers have minor injuries, while the other passenger taken to hospital has chest injuries.

All those who were travelling in the car are thought to be from Victoria.