The world's best MotoGP riders have expressed their sympathy at the death of 19-year-old rider Shoya Tomizawa in a Moto2 race in San Marino on Sunday.

The Japanese rider fell off his bike mid-race and was hit by the bikes of Alex De Angelis and Scott Redding, who both also crashed but walked away relatively unscathed.

Tomizawa received immediate attention from medics and was rushed to hospital where he later died.

Elias team manager Fausto Gresini, who had one of his riders Daijiro Kato die at Suzuka in 2003, said it was a black day for the sport.

"Today is a very sad and very tough day, when racing doesn't feel like it should. I know just how hard it is to lose a rider in these circumstances and I know the pain that his family and all the guys on the team who worked with him are feeling right now. There is little more to say," he said.

MotoGP race winner Dani Pedrosa said words could not describe the tragedy.

"There are no words to say how it feels after this victory - it feels like nothing. It's so sad, terrible, and these things should never happen," he said.

"As a person I can only say that he was a very funny boy, always happy and making jokes, and as a rider he earned respect from everybody in a very short time, he was fast and brave."

Championship leader Jorge Lorenzo said such a tragedy put racing into perspective.

"I don't have many words for the race on such a sad day. 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," Lorenzo said.