A Mitsubishi Lancer travelling on Spring Drive in Mulwala, about 100 kilometres west of Albury, left the road and hit a tree about 4pm on Sunday, police said.

The three-year-old boy died at the scene. The second boy, aged four, was taken to an Albury hospital in a serious but stable condition.

The driver, a 40-year-old man, was flown to hospital in Melbourne for treatment.

Officers from Albury Local Area Command set up a crime scene on Spring Drive and are investigating. They will prepare a report for the coroner.

The fatal crash was one of three across NSW on Sunday.

Earlier in the day, a man died when his motorcycle left the road and hit a tree in the Blue Mountains.

Police said the man, believed to have been aged in his 50s and from Sydney, was riding along Chifley Road west of Darling Causeway at Bell about 10am when the crash occurred.

He died at the scene.

Another man died in a crash near Goulburn just before 5pm on Sunday.

Police said they were called to Gundaroo Road in Gunning, about 50 kilometres west of Goulburn, to reports of a two-car crash.

One of the drivers, a man aged in his 20s, died at the scene. The male driver of the second vehicle was taken to Canberra Hospital in a serious condition. No passengers were in either car.

Police have urged anyone with information about any of the crashes to contact Crime Stoppers on 1800 333 000.

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