A dynamite-laden truck exploded after colliding with another vehicle on a busy highway in northern Mexico's coal country, killing at least 34 people, including three reporters at the scene, state and federal officials said.

Authorities said the two vehicles crashed into each other Sunday evening, drawing a crowd of curious onlookers as well as a small army of police, soldiers, emergency officials and journalists.

Shortly after the crowd arrived, the wreckage caught fire, and the dynamite exploded, sending a ball of fire into the sky that consumed nearby cars and left a 10-by-40 foot crater in the concrete, said Maximo Alberto Neri Lopez, a federal police official.

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He said more than 150 people were injured.

The force of the explosion blew out the windows of a passenger bus a quarter-mile away.

The dead included three newspaper reporters from the nearby city of Monclova, said Luis Horacio de Hoyos of the Coahuila state Attorney General's Office.

It was unclear if the explosive truck's driver was among the dead. Early reports said he might have fled.

Coahuila state has a large mining industry, most of it in coal.

The explosion raised further questions about the safety of Mexican trucks.

This weekend, Mexico began sending its first tractor-trailers across U.S. territory under a long-delayed, NAFTA-mandated program. Before, Mexican trucks were limited to 25-mile zone along the border.

Many in the U.S. fought the change, arguing that Mexican trucks are unsafe.

The truck that exploded in Coahuila did not appear to be headed for the U.S. It had recently left an Orica explosives plant and was headed west to Coquimatlan, Colima, a federal police officer who was not authorized to give his name told The Associated Press by phone.

A woman who answered the phone at Orica's offices in Monclova said all company officials were at a meeting, and she could not comment. The company is based in Australia and has operations in 50 countries across six continents.