Tomizawa was in only his second season of MotoGP
Seven-times MotoGP world champion Valentino Rossi has led the tributes to rider Shoya Tomizawa, who died in Sunday's Moto2 race in San Marino.
"When something so sad like this happens everything else goes to zero - the result doesn't matter," said Rossi.
Tomizawa used bike manufacturer Suter Racing and chief executive Eskil Suter said the rider was extremely popular.
"Shoya was more than a friend. He was like a family member. He was loved by everybody in the paddock," he said.
"I am terribly sorry for his family and his team who suffered this tragic loss."
I'm so sorry for Shoya because he was a strong rider but above all he was very 'sympatico' - he was very funny, always smiling and he always had nice things to say to everyone
Tomizawa died after coming off his bike at the Misano circuit while under pressure from Italy's Alex de Angelis.
Neither De Angelis nor British rider Scott Redding - who like Tomizawa was riding a Suter motorbike - were able to avoid hitting the 19-year-old Japanese.
Eskil Suter insisted de Angelis and Redding, who both also came off their bikes, had no chance of missing Tomizawa.
"I also feel sorry for De Angelis and our rider Scott Redding," said Suter. "After the initial suspicion of a fractured pelvis, Scott was cleared of serious injuries.
"But mentally he is completely shattered even though nothing that happened was his fault. Today was a sad reminder that racing remains dangerous despite all improvements in track safety."
Tomizawa, who rode for the Technomag-CIP team, had completed 15 laps of the Misano circuit before the accident, which happened in dry conditions.
He was treated at the circuit before being taken to the Riccione Hospital on the Adriatic coast where he died.
Tomizawa was in only his second season in the MotoGP world championships and won the Moto2 race at the Qatar Grand Prix, which opened the new season.
He had been in seventh position in the overall standings prior to Sunday's race, which was eventually won by Spain's Toni Elias.
Racing legend Rossi added: "I'm so sorry for Shoya because he was a strong rider but above all he was very 'sympatico'.
"He was very funny, always smiling and he always had nice things to say to everyone.
"He was also very young with a great career ahead of him so we are all very sad."
Repsol Honda rider Andrea Dovizioso, who finished fourth in the top class, said: "It's a huge pity because he was a good guy and a strong rider.
"I am so sad and I just want to say how sorry I am for his family and his friends. When this happens nothing else matters."
Tech 3 Yamaha boss Herve Poncharal, who also runs a team in the Moto2 series, said: "On behalf of everyone at Tech 3 Yamaha, I'd like to send our deepest sympathies to the family and friends of Shoya Tomizawa.
"He was a great talent and a really good guy who will be missed by all of us in the racing community."
Tomizawa was the first rider to be killed during a Grand Prix weekend since compatriot Daijiro Kato died after a crash in the 2003 Japanese Grand Prix at Suzuka.
Tomizawa had taken to wearing a tribute to Kato on the left shoulder of his leathers.