Around 300 people were working at the Blueberry factory when a huge explosion rocked its second floor in Ciudad Juarez, a city bordering the US state of Texas, officials said.

"We are searching for people in the debris. We calculate 20 have disappeared," city government spokesman Guillermo Terrazas told AFP.

Civil protection chief Fernando Motta Allen said 10 of the injured people were in serious condition and another four were in a critical state.

"There is an area which (rescuers) were not able to get to because they are working to control the fire sparked by the damaged boiler," Motta said.

Some 30 ambulances rushed to the scene of the explosion to take the injured to hospitals.

AFP