One motorcyclist has been killed and another two have been seriously injured after a series of horrific motorbike accidents on Illawarra roads at the weekend.

A 24-year-old Chatswood man was killed in the Royal National Park when his motorbike collided head-on with a sedan travelling north on Sir Bertram Stevens Drive  just after midday on Sunday.

Emergency services were unable to revive the man, despite arriving at the accident site soon after.

Shocking photos of the scene show a motorbike crushed under the front passenger wheel of a black sedan, which also has significant damage to its grill and undercarriage.

It appeared the motorcyclist, who was travelling south, failed to negotiate a sweeping left-hand turn, Ambulance NSW Illawarra duty operations manager Inspector Norm Rees said.

Two hours later, Insp Rees attended an accident at the hairpin bend on Bulli Pass, where a 23-year-old woman had been thrown from her motorbike.

She was taken to Wollongong Hospital in a stable condition, suffering a suspected fracture to the left leg and dislocated left elbow.

It was the third motorbike accident he attended at the weekend.

On Saturday morning, witnesses rushed to help a 42-year-old Springfield man who crashed his motorbike into a power pole at Austinmer, snapping the vehicle in two.

The man suffered significant leg fractures as a result of the crash, which happened about 11am on Lawrence Hargrave Drive.

Austinmer Cafe owner Adrian Naccari said diners leapt from their seats to assist the man.

“It shook people up, it’s not a nice thing to see,” Mr Naccari said.

“He was just lying flat on his back and getting first aid.

“People were talking to him and he was responding, which was good.”

Insp Rees said witnesses had reported the man’s bike started wobbling before it smashed into the pole.

Pieces of the bike were found some distance from the site of the actual crash.

“Witnesses state they saw a bike travelling from south to north at a high speed,” Insp Rees said. 

“Apparently, as he was coming down into the dip he had what they call the death wobbles – the bike was jumping all over the place – he’s lost control and hit a pole.”

The man was taken by road to St George Hospital, after strong winds made it impossible for the rescue helicopter to take off, Insp Rees said.

He was in a stable condition on Sunday. Insp Rees urged ‘‘weekend warrior’’ motorcyclists to drive safely on northern Illawarra roads.

‘‘Being a bike rider myself, I appreciate windy roads [offer] ideal riding conditions, but people have just got to slow down.’’