A truck that exploded and caused an elevated stretch of highway to collapse in central China, killing 10 people, was loaded with holiday fireworks that were illegally produced and transported, authorities said.Local authorities have shut down the company that made the fireworks, Hongsheng Fireworks Manufacturing Co. Ltd., and detained four company officials following Friday’s blast, state media reported.It remained unclear what set off the fireworks as they were shipped eastward on a major highway through Henan province. State-run China Central Television said witnesses believed a collision caused by heavy smog might have triggered the blast, which occurred about 90 kilometers (55 miles) west of the ancient city of Luoyang.The Ministry of Public Security said Hongsheng, based in the neighboring province of Shaanxi, had illegally produced the explosives.Agencies