The 24-year-old - nicknamed Sic - lost control of his Honda at turn 11 and swerved across the track, straight into the path of American rider Colin Edwards and compatriot Valentino Rossi.
Simoncelli's helmet came off in the collision and he was taken to the medical centre where he was declared dead.
A photograph of the Italian on his motorbike covers the front page of Gazzetta dello Sport with the headline: "Sic 1987-2011."
Gazzetta's editorial describes the pain felt by everyone who knew Simoncelli.
The Italian's death was the first fatality in the MotoGP since Japan's Daijiro Katoh died from injuries sustained at the 2003 Japanese Grand Prix.
Coriere dello Sport has a photograph of Simoncelli with the headline: "Ciao Great Marco.
"Tragedy in Sepang. Simoncelli dies, a true champion but especially a wonderful man that will be missed by everyone."
Tuttosport focuses on Simoncelli's passion for the sport that took his life.
The Turin-based sports newspaper also leads with Simoncelli's death with the headline: "Sic love does not die."
National newspaper La Repubblica has a photograph of the accident on the front page followed by a caption which reads: "Moto shock, Simoncelli dies on the track."
The article adds: "Marco never liked losing, he always risked at the final turn."
La Repubblica's editorial also describes the risk taken by riders in the sport.
It reads: "Fractured vertebrae, a sign of a wheel on his neck, a heart that goes into shock, injuries to his head and thorax.
"That's how a MotoGP rider dies: run over by his sport brothers, by his most loved rider (Rossi), on a Sunday morning in which the rest of the world was sleeping."
Il Messagero newspaper also shows images of the accident on the front page.
"Tragedy on the track. Simoncelli dies. Valentino cries "he was like a brother to me".
The newspaper highlights Rossi's pain in the tragedy.
"Rossi's sense of blame. A friend of Valentino, Simoncelli finished underneath his wheels.
"But Rossi is not at fault. Simoncelli died because of electronics."
The newspapers suggests a technical fault may have contributed to the accident.
Simoncelli's crash will be investigated.