SAN JUAN DE SABINAS, Mexico — Rescue workers were burrowing through debris clogging a Mexican coal mine early today in a desperate effort to reach some 65 miners who were trapped for more than a day by a gas explosion.

The miners were carrying only six hours of oxygen with them when the explosion occurred early Sunday, and officials said it was unclear if they had access to fresh air. Rescue teams had failed to make any contact with the trapped miners.

Several other workers who were near the mine's entrance at the time of the explosion were able to escape alive and were treated for broken bones and burns.

Rescue teams worked round-the-clock as family members waited for news, huddled near bonfires and wrapped in blankets to protect against the bitter cold outside the mine near the town of San Juan de Sabinas, 85 miles southwest of Eagle Pass, Texas.

Officials had promised a pre-dawn briefing, but they had yet to appear and were not letting anyone in the security zone.

Sergio Robles, director of Coahuila state's emergency services, said the miners were carrying six hours of oxygen with them and were located between one and three miles from the mine's entrance.

He said rescue officials had advanced up to 300 yards into the mine after working for nearly 20 hours. The explosion occurred around 2:30 a.m. Sunday. It was unclear when they would reach the miners.

Rescue efforts were slowed by the presence of toxic gases, including carbon monoxide, Robles said. When asked if officials believed the miners survived the explosion, Robles said: "It would be difficult because of the presence of gas. But we are holding out hope of finding someone alive."

Juan Rebolledo, vice president of international affairs for mining giant Grupo Mexico, which owns the mine, said oxygen tanks were scattered throughout the site, but it was impossible to know if the trapped miners had access to any of them.

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

Rebolledo said several rescue teams were taking turns carefully removing debris that had clogged the steep shaft.

"It's slow work because of the quantity of debris," he said.

Worried family members waited for any information about their loved ones.

"We have hope that they are alive because they tell us that they have fans working" to ventilate the mine, said Olivia Camarillo, 50, whose 27-year-old son was trapped.

Norma Vitela heard about the explosion on the radio and came to find out what happened to her husband, 47-year-old Jose Angel Guzman. A father of four, Guzman had worked in the mine for 16 years, earning about $75 a week.

"Now we are waiting for a miracle from God," she said.

Vitela said her husband had mentioned before that there were problems with gas in the mine, but he couldn't afford to quit.

Consuelo Aguilar, a spokeswoman for the National Miners' Union, said there had 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.

She called for an investigation to determine the exact 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," he said.

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

Pedro Camarillo, a federal labor official who was not related to Olivia Camarillo, told reporters during a news conference at the site that officials found nothing unusual during a routine evaluation on Feb. 7.

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

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 United States. Two men died in a fire Jan. 21 at a mine in Melville, nearly three weeks after 12 men died after an explosion near Tallmansville.

U.S. rules require miners to carry oxygen tanks that provide only about an hour's worth of air. There is evidence that some of the miners killed in the Jan. 2 Sago mine accident used their oxygen devices, yet it took rescuers more than 40 hours to bring the victims above ground.

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.