Mitsubishi Motors admitted Wednesday to falsifying fuel-economy test data on more than 600,000 vehicles. The Japanese automaker’s shares tumbled more than 15 percent—the most in more than a decade—after the announcement. The company said it had halted the production and sale of the affected vehicles and has created an independent panel to investigate. Mitsubishi Motors President Tetsuro Aikawa said the misconduct was reported to Japan’s transportation ministry. The manipulated data involved 157,000 of Mitsubishi light passenger cars and 468,000 vehicles produced for Nissan. Mitsubishi launched an internal investigation after Nissan reported inconsistencies in emissions data. The investigation found that figures had been falsified. Mitsubishi’s announcement follows the Volkswagen emissions scandal that rocked the industry last year, when the German automaker admitted to cheating diesel emissions tests.