Just moments after the start of the race, one bike wobbled before going down and skidding towards the middle of track as the riders exited the first corner.
That led to a collision that eventually became an 11-bike crash with oncoming riders unable to avoid the fallen bikes.
The race was being broadcast live on TNT Sports but cameras cut away from the track following the crash.
Motorsport Vision Racing (MSVR), who are responsible for circuit operations at Oulton Park in Cheshire, said Jenner was treated at the track but died from “a catastrophic head injury.”
Richardson was also treated at the track and taken to Royal Stoke University Hospital with severe chest injuries but he died prior to arrival.
Tunstall, 47, is in hospital with “significant back and abdominal injuries” while five riders suffered minor injuries and the other three were not injured.
Simon Patterson, a MotoGP journalist, told BBC Radio 5 Live: “It just seems there’s been a chain-reaction on the exit of turn one of Oulton Park, which isn’t a particularly scary or aggressive corner.
“But unfortunately, as we’ve seen multiple times all around the world, as motorcycle racing has become safer, as organisers have done more to reduce the risk of injuries in bike racing, the one thing that is very, very difficult to protect against is when you get multiple riders falling together and the risk of people getting struck by oncoming machinery.
“I think that’s exactly what’s happened in this situation. It’s super unusual to see so many riders fall together.”
