Four Air Ambulances were called out to Olivers Mount in Scarborough after two separate crashes.
The first, at about 10.30am, saw a bike rider crash into spectators during a qualifying session for the Gold Cup event.
Three people were taken to hospital as two Air Ambulances landed and three road ambulances were called. One person is thought to have been seriously injured.
Then, at 1.40pm, a second, entirely separate crash occurred, where a bike rider crashed through a fence and hit spectators.
Three people were taken to hospital from that incident including the rider of the motorbike and another two spectators.
In total, four air ambulances and six road ambulances were called out, as well as three clinical supervisors.
The race was cancelled after the second incident.
Olivers Mount Racing issued this statement: "Today we have had two serious incidents involving a number of spectators.
"Our medical personnel, together with the marshals and officials of the club, local police, nhs, ambulance staff and helimeds have treated all the injured.
"In view of the seriousness of these incidents and our requirements to call on outside assistance to help with this treatment, we have reluctantly taken the advice of everyone concerned and have decided to cancel the rest of the meeting.
"We sincerely apologise to you all for taking this decision and hope you will understand our difficulties in this unprecedented situation.
"We wish you all a safe journey home.
"The club will be making a full statement in due course."