Three killed and one seriously injured in horror day on NSW roads

A pedestrian, a motorcyclist and a driver have lost their lives in a single day on NSW roads.

Rescuers were called to a crash scene on Bassett Street, in Sydney's Mona Vale, shortly before 8pm on Wednesday after a Nissan Cefiro hit a tree.

Police say the driver, a man believed to be aged in his 20s, died at the scene.

He is yet to be formally identified. His passenger was taken to Royal North Shore Hospital with minor injuries

Earlier on Wednesday, a man was fatally hit by a road train near the NSW-Victoria border, on the Cobb Highway at Moama.

Police say he sustained severe head injuries.

The truck driver was taken to Deniliquin Hospital for mandatory blood and urine tests.

In another fatal incident, about 6am, a motorcycle and a truck collided at Maclean on the state's north coast.

The truck driver was uninjured but the motorcyclist died at the scene.

Also on Wednesday, a 90-year-old man was struck by a private school bus at Appian Way, in the inner western Sydney suburb of Burwood, as dozens of children watched on.

Police have been told the man was standing beside his parked car when he was hit.

He was taken to Royal Prince Alfred Hospital, where he remained in a serious but stable condition on Wednesday evening.