A rider has died and another was seriously injured in two separate incidents at a quad and motocross event.
Durham Police said they had "no choice" but to shut down the meeting at Hardwick Hall Hotel, near Sedgefield, on safety grounds following the fatality and second injury.
A spokesman said the first incident happened shortly after 1pm on Sunday when a male rider came off his bike and suffered critical injuries.
He was taken by air ambulance to the James Cook University Hospital, in Middlesbrough, but was confirmed dead shortly after arrival.
The spokesman said a woman was then hurt in a separate incident just before 2.10pm. The female rider, thought to be in her early 30s, was also taken by air ambulance to the same hospital with what are believed to be serious injuries.
He said that officers took the decision to close down the privately-run event, which involved around 100 participants and 300 spectators, on safety grounds.
Superintendent Mick Bird said: "We understand the formal investigation is likely to be led by the local authority but we are carrying out initial inquiries into the circumstances.
"With two very serious incidents within little more than an hour, we felt there was little choice but to bring the event to a close."