A rider at Olivers Mount crashed through a fence and hit spectators, according to a spokesman for Yorkshire Ambulance Service.
Two Air Ambulances landed - for the second time today - and three road ambulances were also called.
Two spectators were taken to hospital in Scarborough, while the rider was airlifted to James Cook Hospital in Middlesbrough.
A North Yorkshire Police spokesman said: "Police were called to a second collision at Oliver’s Mount circuit at around 1.45pm on Sunday 24 September 2017.
"There are a number of casualties.
"We will provide further information when we are able."