Thirteen people were injured, two critically, after a car crashed into a crowd during a demolition derby in southeastern Australia, police said.

The car had been taking part in a race in the town of Walcha on Saturday night when it drove through a fence and hit the grandstand, New South Wales police said in a statement.

The race, part of the annual Walcha Motorcycle Rally, had been a demolition derby - a type of motorsport where drivers ram their vehicles into one another.

Brendan Moylan, a member of parliament for Northern Tablelands, the region where Walcha is located, said on social media on Sunday that nine people remained in hospital and "all are now recovering".

Earlier, police put the number of injured at nine. They said the ages of the injured bystanders ranged from 20 to 75, while a critically injured person was a 54-year-old man. An investigation was under way, they said.

Police said they were told that the 27-year-old driver of the car had been involved in a collision on the track right before it drove into the fence.

In a statement published on the Walcha Motorcycle Rally's Facebook page, the Walcha Council said that it was "shocked and stunned at the unfortunate accident".

The Council said it would work with authorities to "examine the circumstances which led to the accident".

Giving any comments before concluding the inquiries would be "inappropriate", it said.

In a post on Facebook, Moylan thanked emergency responders and other bystanders for their "swift and incredibly professional work at the scene".

"My thoughts are with everyone affected," he wrote.

Barnaby Joyce, former deputy prime minister and incumbent New England lawmaker, wrote on Facebook that his "thoughts, prayer and hopes" were with those injured in the crash.

"Such a sad end to such a great event," he wrote.

The Walcha Motorcycle Rally describes itself as a "grassroots event for motorcycle enthusiasts". (BBC)

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