At least seven miners have been killed in a gas explosion at a coal mine in northern Mexico.

The miners, aged between 20 and 39, suffered severe burns and were crushed by falling rock on Wednesday, said Francisco Contreras Obregon, the head of the civil defence force in northern Coahuila state.

The explosion took place at the "El Progreso" mine, 150km southwest of the border city of Eagle Pass, in the US state of Texas.

The bodies of seven miners have been recovered, who were trapped underground after what appears to have been a methane gas explosion.

Emergency services brought the bodies of the men, to the surface after an hours-long rescue effort, said Juan Antonio Ibarra, a emergency services official.

"Sometimes these mines don't have the appropriate security measures," said Ibarra.

Lacking safety measures

He said a pocket of gas likely caused the explosion that occurred 75 meters underground.

The rescue operation, which involved up to 50 people, had moved slowly because of the need to ventilate the mine to prevent another explosion, said Ibarra.

The "pozito," or little hole, coal mine, which is privately operated by the El Progreso mining company, has faced fines and sanctions in the past, the Mexico's labour ministry said in a statement.

The mine had been inspected 16 times since 2009 and access restrictions were enacted as recently as June after inspectors found it lacked emergency exits, the labour ministry added.

Methane gas is a frequent hazard in coal mines, especially the kind of primitive, small-scale mines that cover the Coahuila state.

In 2006 65 miners died in an explosion at another Coahuila coal mine site.

Source: Agencies