The Belgian Grand Prix was stopped after five laps following a massive crash involving Brazilian Luciano Burti.
Burti's Prost careered at high speed straight into a tyre barrier after dicing with the Jaguar of Eddie Irvine.
The Prost was forced onto the grass as Irvine tried to go past at Blanchimont, one of the fastest and most dangerous stretches of the circuit, and lost its front wing.
It then plunged across the track and, without losing speed, ploughed straight into the barriers in a cloud of debris.
Irvine, his friend and former team mate at Jaguar, joined in the efforts to shift tyres off the Prost as medical staff rushed to the scene.
A curtain was erected around the car and the race continued briefly behind a safety car before being halted.
Initial reports from race control said Burti was conscious and "O.K.".
The race had an eventful start before then, with Colombian Juan Pablo Montoya going from pole position to the back of the grid after stalling on the second of two formation laps.
The Williams driver, who had beaten team mate Ralf Schumacher for pole, waved his hands at the front to alert marshals.
He was then left stranded as the rest of the field set off on what was already the day's second formation lap.
The Prost of German Heinz-Harald Frentzen had stalled earlier, forcing the first start to be aborted and reducing the race to 43 laps.
Ferrari's Michael Schumacher, seeking a record 52nd career win, was leading when the race was stopped.