Video posted on social media showed the moment the car crashed through the barrier and into the grandstand.
Police have been told that the 27-year-old driver was involved in an on-track collision immediately before the car crashed into the crowd.
National Party MP Barnaby Joyce led a chorus of well-wishes on social media.
“My thoughts, prayers and hopes are with those now in critical care after the incident at Walcha tonight after a vehicle in the derby collided with spectators,” Joyce said on Facebook.
“Thank you to all the off-duty nurses and first responders who immediately dropped everything to help the injured in the storm. Such a sad end to such a great event.”
Another person said on social media: “Heartbreaking to hear of the Walcha tragedy tonight … my prayers are with you all… pray for the community and those impacted.”
The NSW Police specialist Crash Investigation Unit will examine the crash scene.
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