The official Xinhua News Agency said nine people were confirmed dead and another 13 injured, including four in serious condition. It said the collapse smashed and buried at least 25 vehicles.
Earlier reports by China National Radio and some other outlets of 26 people killed were later removed from websites, without explanation.
A 260-foot stretch of a major east-west highway collapsed in Mianchi county in Henan province. It scattered blackened chunks of debris and shattered the windows of a nearby truck stop.
Photos posted online by Xinhua showed a stretch of elevated highway gone, with one truck's back wheels perched at the edge of a shorn-off section of the highway. Other photos showed firefighters below spraying water on scorched hunks of concrete, wrecked trucks and flattened shipping containers.
There was no immediate word on the cause of the explosion. It occurred about 55 miles west of Luoyang, an ancient capital of China known for grottoes of Buddhist statues carved from limestone cliffs.
Fireworks are an enormously popular part of Chinese Lunar New Year festivities. To meet the demand, fireworks are made, shipped and stored in large quantities, sometimes in unsafe conditions.A result is periodic catastrophe: In 2006, on the first day of the Lunar New Year, a storeroom of fireworks exploded at a temple fair in Henan, killing 36 people and injuring dozens more. In 2000, an unlicensed fireworks factory in southern China exploded, killing 33 people, including 13 primary and secondary school students working there.