Chinese authorities say a truck that exploded and caused an elevated stretch of highway to collapse, killing 10 people, was loaded with holiday fireworks that were illegally produced and transported.

State media say local authorities have shut down the factory where the fireworks were produced and detained four company officials after Friday's blast.

It is unclear what set off the fireworks on its shipping route through the central province of Henan.

The Ministry of Public Security said Saturday that Hongsheng Fireworks Manufacturing Co. Ltd., based in neighboring Shaanxi province, illegally produced the explosives, improperly packaged them and contracted with a trucking company unlicensed to handle hazardous commodities.

Fireworks are a major part of the festivities surrounding the Chinese Lunar New Year, which falls on Feb. 10 this year.