HONG KONG — A truck laden with fireworks exploded on an elevated expressway in central China on Friday, unleashing a blast that threw vehicles 30 yards to the ground below and killing at least nine people, state news reports said.

The truck was on an expressway near Sanmenxia in Henan Province in morning fog when the it erupted, causing an 87-yard section of the Yichang Bridge to collapse, according to the Web site of Dahe Daily, a newspaper in Henan, which quoted rescue officials at the site. Earlier, officials had raised the possibility that a bridge collapse set off the explosion.

Fireworks play a large role in China’s traditional Lunar New Year celebrations, which begin Feb. 9, and the explosion was a reminder of the dangers brought by the crush of people and goods on the move before the holiday.