The head of Porsche's archives, Dieter Landenberger, said the firm would arrange an independent historical investigation to check evidence gathered by journalist Ulrich Viehöver in a new book about the city of Stuttgart's role in the Nazi era.
Landenberger told the Israeli newspaper Haaretz: "Until now, we thought our total had been was much lower."
Porsche has previously accepted that it used about 50 forced labourers and Landenberger professed surprise at the new information.
In the book's chapter on motoring pioneer Ferdinand Porsche, he writes of several hundred forced labourers, including prisoners of war, who had worked for company.
Landenberger vowed that the company was taking the new claims absolutely seriously. The investigation will begin this year, he said.
In his eagerness to make Germany a nation of motorists, Adolf Hitler contracted Ferdinand Porsche to make a car for the people. The result was the Volkswagen Beetle, on which the earlier Porsche brand's designs were based.