The BBC's Peter Greste: "It is still not clear what started the carnage"

The disaster happened in a crowded market area in the central town of Celaya.

"It's a major tragedy," said Celaya's mayor Ricardo Suarez in a TV interview.

Reports suggest the first explosion occurred in a fireworks warehouse across the street from the city bus station.

Emergency services were at the scene attempting to put out the fire when the area was hit by further explosions.

The blaze is thought to have caused cooking gas tanks in nearby restaurants to ignite.

Some firefighters are reported to have been killed in the later blasts.

Army called in

Casualties lined the streets

Among those killed were a police officer, two Red Cross workers, two fire fighters, a local reporter and four children.

Troops were called in to help police evacuate residents and to seal off the area around the explosions, as rescue workers searched for more victims.

Electricity supplies were cut off, and officials banned the sale of petrol throughout the city until the smouldering site had been dampened down.

Grief and shock in the aftermath of the blasts

Officials of Guanajuato state appealed for help from neighbouring areas and urged any available doctor to report at the local hospitals.

The Governor of Guanajuato state, Martin Huerta, urged residents not to interfere with rescue operations.

Celaya is an industrial city in Guanajuato state about 200km (120 miles) northwest of Mexico City.

Among other things, it produces fireworks, which play an important part in Mexico's many fiestas and celebrations.