Police and the Ministry of Labour in Cambodia are investigating a mass fainting of about 800 workers at two factories that produce footwear for the German sporting goods group Puma.
One person taken to hospital spoke of feeling exhausted and dizzy.
Another said the smell from materials used in the manufacturing of sport shoes may have made them sick.
Phnom Penh police chief Touch Naruth said it could have been that the workers were too tired. Environment issues would also be looked at and whether there was enough air or oxygen.
Manufacturing of garments is Cambodia's third-biggest currency earner after agriculture and tourism.