Two riders have died after an 11-bike crash during a British Supersport Championship race at Oulton Park on Monday.
Englishman Owen Jenner, 21, and Shane Richardson, 29, of New Zealand, were fatally injured in a "major chain reaction" incident on the first lap of the race as the riders exited turn one.
The race, the third of the weekend, was halted on the first lap, with series director Stuart Higgs later calling the incident "severe and catastrophic" as he announced the event had been cancelled.
In a statement on Monday night, Motorsport Vision Racing (MSVR), who are responsible for circuit operations at Oulton Park, said another rider, Tom Tunstall, had sustained "significant injuries".
"Owen Jenner, 21, was initially treated trackside and then taken to the circuit medical centre, where despite further resuscitation treatment he died from a catastrophic head injury," MSVR said.
"Shane Richardson, 29, was initially treated trackside and then taken to the circuit medical centre before being transferred to Royal Stoke University Hospital with severe chest injuries. He died prior to arrival.
"Tom Tunstall, 47, was initially treated on the track and was taken to the circuit medical centre, he was later transferred to Royal Stoke University Hospital with significant back and abdominal injuries.
Riders Carl Harris, Max Morgan, Cameron Hall, Freddie Barnes and Morgan McLaren-Wood were treated for minor injuries at the circuit medical centre.
Lewis Jones, Corey Tinker and George Edwards were also involved in the accident but did not suffer injury.
MSVR and the Motorcycle Racing Control Board said they are "investigating the full circumstances of the incident in conjunction with the Coroner and Cheshire Constabulary".
Race one of the meeting took place on Sunday with Bradley Ray claiming victory, before Leon Haslam secured his first win since 2018 in Monday's sprint.
The Supersport Championship is a support class to the main British Superbike series.
Oulton Park in Cheshire was hosting the first round of the 2025 championship.