Nine people were killed and another 11 injured as of press time, after part of an expressway viaduct in Sanmenxia, Central China's Henan Province collapsed Friday, with an explosion involving a truck loaded with fireworks being blamed, according to the initial investigations by local authorities.

The explosion, which occurred around 9 am Friday, happened right in the middle of the Spring Festival travel rush that sees hundreds of millions of Chinese people traveling home for the traditional holiday, which this year falls on February 10.

At least 25 vehicles were seen falling from heights of 30 meters off the partially destroyed 80-meter-long viaduct, which is on a section of the G30 expressway which links Lianyungang in East China's Jiangsu Province to Horgos, a border port of the Xinjiang Uyghur Autonomous Region in the country's far west.

The emergency office in the city of Sanmenxia said the collapse was caused by a fireworks explosion.

By late Friday, six trucks and two small passenger cars has been hoisted from the scene, said local authorities in a statement.

Ren Zhanzhou, deputy director of the publicity department of the CPC Sanmenxia City Committee, told the Global Times that at least four of the injured were in critical condition and they are all undergoing medical treatment. "Some 160 rescuers have been sent to the scene. We are still trying our best to search for the injured. The situation at the scene had been complicated by recent cold, foggy weather."

A truck driver who was around 20 meters away from the scene told China Central Television that he heard a loud sound and saw small balls of fire drop off the viaduct. Some local residents living nearby said the window glasses of their homes were shattered by the fierce explosion.

The Zhengzhou-based Dahe Daily quoted an injured passenger as saying that the truck loaded with fireworks exploded after it was hit by many vehicles from behind.

The Ministry of Public Security held an emergency meeting Friday afternoon during which it pledged to intensify the supervision of fireworks and ensure safety.

Li Daguang, a professor and expert in army facilities from the National Defense University of the People's Liberation Army, told the Global Times that a load of fireworks would be powerful enough to tear the viaduct into pieces, and in certain circumstances, could even potentially destroy a house. "Those fireworks are just like explosives," he said.

Local officials said they had launched emergency plans to divert traffic flows to nearby roads to minimize the impact brought about by the accident, meanwhile, the Zhengzhou railway bureau said they had added eight more temporary trains to ease the traffic burden. 

At least 14 bridges have collapsed across the country since 2007, caixin.com reported, raising public concerns over the quality of infrastructure and construction codes.

In a separate accident on Friday, a coach bus rolled down into a valley in Luzhou, Southwest China's Sichuan Province in the afternoon, killing 7 passengers and injuring another 22.