Tomizawa was in only his second season in the world championships
Moto2 rider Shoya Tomizawa has died from multiple injuries after a crash at the San Marino Grand Prix.
The 19-year-old from Japan came off his bike when under pressure from Italy's Alex de Angelis at the Misano circuit.
Neither De Angelis nor British rider Scott Redding were able to avoid hitting Tomizawa, but the race was allowed to continue.
Tomizawa was treated at the circuit and then taken to the Riccione Hospital on the Adriatic coast where he died.
He had completed 15 laps before the accident, which happened in dry conditions.
The race continued and the riders were informed of Tomizawa's death after it finished.
A statement on the MotoGP website said Tomizawa sustained fatal injuries to his head, chest and abdominal areas.
It added: "Everybody involved in MotoGP extends its deepest condolences to Shoya's family and friends at this tragic loss."
De Angelis described the crash as "the worst ever incident in my career".
The Italian added: "I saw Shoya fall in front of me. I tried everything I could to avoid him and hit his motorbike instead.
"I'm truly devastated about what happened to Shoya. I'm close to his family and all of them loved him a lot. In moments like this nothing seems to matter."
De Angelis received medical treatment at the track and was not taken to hospital.
Dani Pedrosa, who won the MotoGP race held after Tomizawa's, told BBC Sport: "I have a big hole here, everything is empty. I feel so strange."
And MotoGP champion Valentino Rossi stated he had seen the "terrifying" crash on television.
"I understand from the first moment it was bad," said the Italian. "But then you have to try to concentrate in the race. When it happens like this, all the rest is nothing."
Tomizawa's death follows that of 13-year-old Peter Lenz in a warm-up event ahead of the Indianapolis MotoGP on 29 August. He also crashed and was hit by another rider.
MotoGP drivers sombre after tragic day
Prior to this weekend, Japan's Daijiro Kato was the last MotoGP rider to die after an accident. He crashed during the first race of the 2003 season at Suzuka and died following two weeks in a coma.
Tomizawa was in only his second season in the MotoGP world championships and had won the Moto2 Qatar Grand Prix, which opened the new season. He had been in seventh position in the overall standings.
Redding was taken to hospital after Sunday's crash but is not thought to be seriously injured. The race was won by Toni Elias of Spain.