Three dead in horror hour on NSW roads

A cyclist and two drivers have been killed in the space of an hour in a horror Sunday morning on NSW roads.

A 22-year-old died just after 8am when his car veered off the Hume Highway at Gundagai, 100km west of Canberra.

The Hyundai Elantra hit a railing and the man died at the scene.

Half an hour later, a cyclist aged in his 40s fell from his bike in northwestern Sydney and was struck by a passing motorbike.

The man had been competing in the annual Tour De Hills race with about 700 others when his bike was apparently clipped by another rider at 8.30am. He died at the scene.

Around the same time, about 150km west, a Holden ute hit a tree and burst into flames near Oberon, killing the driver.

No details on the driver's identity have been released.

Earlier, a 21-year-old was killed when his Peugeot convertible slammed into a tree in the Royal National Park, south of Sydney, around midnight.

He died at the scene but his passenger, also 21, was airlifted to St George Hospital where he remains.

All four deaths were avoidable, said Traffic and Highway Patrol Commander, Assistant Commissioner John Hartley.

"Driving distracted, tired, under the influence of alcohol or drugs, and failing to wear seat belts or correct helmets can easily lead to a fatal crash in a split second," he said.