Italian motorcyclist Dario Cecconi is in a critical condition after an accident at the Tandragee 100 Road Race meeting.
It happened at the Old Clare Road junction of the Markethill Road in the town, which has been closed as far as Bells Crossroads.
Thousands of visitors have been in the town today for the annual Tandragee 100.
Diversions were put in place and motorists should avoid the area.
The collision happened on the Senior Support race and both Superbike and Supertwin events were then called off.
Thirty-eight-year-old Cecconi, who has travelled to Ireland to race on various occasions over the years, was taken to hospital.
Eyewitnesses say he was escorted by ambulance under police escort. Another rider involved in the same incident was not injured.
The motorcyclist’s condition has been described as critical.
The Old Clare Rd junction of the Markethill Rd in Tandragee has been closed to Bellcross Rd following a RTC.
— PSNI Road Policing (@PSNITraffic) April 22, 2017