Mexican police are investigating the explosion of a truck carrying ammonium nitrate that is now known to have killed at least 28 people.
More than 60 homes were wrecked in the blast
Officials initially said more than 30 people had died in Sunday's blast in the northern state of Coahuila.
The truck had been involved in a collision with another vehicle.
Many of those killed were believed to be onlookers and emergency personnel who were at the scene of the accident when the vehicle exploded.
Initial reports said the truck was carrying dynamite but officials said it was loaded with 25 tonnes of a form of the chemical ammonium nitrate, commonly used as a fertiliser but which can also be used to make explosives.
The blast left a 15m-wide (40ft) crater in the road, police said.
Local officials said the truck and another vehicle crashed into one another on a busy road between Monclova, some 850km (530 miles) north of Mexico City, and Cuatro Cienagas on Sunday evening.
The accident drew a crowd of local residents, as well as police, firefighters and local reporters. Three journalists were among the dead.
The wreckage caught fire about half an hour after the crash, sending flames shooting into the air, a police spokesman said.
"I saw pieces of the truck flying through the air all over the place," Mata Castillo, who was driving on the road at the time, told the Associated Press news agency.
More than 150 people were injured and some 50 remained in hospital on Tuesday, several in a serious condition, Mexican media reported.
More than 60 buildings and 50 vehicles were damaged in the explosion.
Police said they had not established the cause of the initial collision as everyone who had witnessed the accident had died.