Emergency officials were tunnelling through the debris hoping the miners had access to air and had survived.

At least eight other miners were rescued and treated at a local hospital for burns and broken bones, union and company officials said.

The injured were near the mine's exit when the explosion occurred on Sunday and were able to escape.

Union and company officials said they believed there were 65 miners trapped in throughout the mine, near the town of San Juan de Sabinas, 135km southwest of Eagle Pass, Texas.

Rescue officials had not been able to make contact with the miners.

Clogging debris

Juan Rebolledo, vice-president of international affairs for mining giant Grupo Mexico, which owns the mine, said several rescue teams were taking turns removing debris that had clogged the steep shaft.

"It's slow work because of the quantity of debris," he said. Officials were planning to work throughout the night.

Sergio Robles, director of Coahuila state's emergency services, said the miners were carrying six hours of oxygen and were between two and five kilometres from the mine's entrance.

He said rescue workers had advanced up to 300m into the mine after working for nearly 20 hours. It was unclear when they would reach the miners. The explosion occurred at about 2.30am (0830 GMT) on Sunday.

Toxic gases

Rescue efforts were slowed by toxic gases, including carbon monoxide, Robles said.

Relatives sit through the night
awaiting news of the miners

When asked if officials believed the miners survived, Robles said: "It would be difficult because of the presence of gas. But we are holding out hope of finding someone alive."

Rebolledo said oxygen tanks were scattered throughout the mine.

Coahuila Governor Humberto Moreira Valdes, who was at the site overseeing the rescue operation, told Televisa network that the mine's ventilation system was still working.

Officials had cordoned off the area, and worried family members waited outside the security zone for information.

Consuelo Aguilar, a spokeswoman for the National Miners' Union, said union officials were also at the scene to assist.

She said there has been concern over safety conditions in Grupo Mexico mines.

"We have pressured for better safety conditions as well as for better pay at the mines," she said.

Investigation

She called for an investigation to determine the cause of the accident and the responsibility of any company officials.

Rebolledo said safety conditions at the mine met Mexican government requirements as well as international standards.

"We follow all the best safety procedures, but accidents can always happen"

Juan Rebolledo,
Vice-president of international affairs, Grupo Mexico

"We follow all the best safety procedures, but accidents can always happen," Rebolledo said.

The company discusses safety conditions with the union in annual meetings and there has been no major disagreement on the issue, he said.

As well as mining coal, Grupo Mexico is the world's third-largest copper producer, with operations in Mexico, Peru and the United States.

Disaster record

There have been various fatal mining accidents in Coahuila.

The worst was in 1969 when more than 153 miners were killed in a pit at the village of Barroteran.

In 2001, another 12 people died in an accident at a mine near Barroteran.
 
Last month, 14 miners died in two separate accidents at mines in West Virginia, in the US. Two men died in a fire on 21 January at a mine in Melville, nearly three weeks after 12 men died after an explosion near Tallmansville.

In Canada last month, 72 potash miners walked away from an underground fire and toxic smoke after being locked down overnight in airtight chambers packed with enough oxygen, food and water for several days.