A truck loaded with ammonium nitrate that exploded Sunday evening in northern Mexico was not licensed to carry explosives, according to the San Antonio Express-News.

The massive explosion killed at least 28 people and injured 130 more – although some accounts place the death toll at 37 with 150 injured.

A witness told reporters the dynamite truck crashed as it was trying to overtake a pickup truck on a highway near Monclova.

The witness said the unidentified truck driver yelled that he was carrying explosives and then fled the scene, the Express-News reported.

About 40 minutes later – as emergency workers, reporters and onlookers were gathered around the wreck – the truck caught fire and exploded.