Mexican crews tunneled feverishly Monday through dirt and rock to reach 65 coal miners trapped by a gas explosion 600 feet underground. Relatives grew increasingly desperate after nightfall with no word of their loved ones.

Some of the miners' family members, who had been camped outside the pit for more than 36 hours, called through a megaphone for more information.

"Tell us the truth!" one man shouted.

Officials said that while prospects were dim, there was still a chance of finding survivors from Sunday morning's explosion at the Pasta de Conchos mine near the town of San Juan de Sabinas, 85 miles southwest of Eagle Pass, Texas.

The trapped men had carried only six hours of oxygen, but officials said they believed a ventilation system that uses huge fans to pump in fresh air and suck out dangerous gases was still working. Even so, they could not be certain the precious oxygen was arriving to where the miners were trapped.

Jesus de Leon, 50, whose 35-year old son is trapped said the wait is unbearable.

"If the rescue workers have advanced just one more meter we need to know about it," De Leon said. "They don't tell us anything."

Some relatives prayed with priests and pastors who joined them at the pit entrance.

Women wept openly and swayed with their arms in the air as the religious leaders spoke, and men wiped tears from their eyes.

"We are waiting for a miracle from God," said Norma Vitela, whose trapped husband, Jose Angel Guzman, had previously told her of problems with gas in the mine. She said the father of four, who earns $75 a week, could not afford to quit.

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

More than 35 hours of digging had pushed rescue teams 400 yards into the mine, about 100 yards from where two conveyor belt operators were believed to be trapped, said Sergio Robles, director of emergency services for Coahuila state.

But others were thought to be trapped as far as one to three miles from the mine's entrance.

Robles said rescuers avoided using electric or gas-powered machinery because of the presence of explosive gases. Medical doctors were on the site to examine rescue workers as they emerged from their eight-hour shifts in the tunnels.

At least a dozen workers who were near the entrance at the time of the explosion were able to escape. They were treated for broken bones and burns.

Asked whether he believed there were more survivors, Robles said: "It would be difficult because of the presence of gas. But we are holding out hope of finding someone alive."

The explosion occurred around 2:30 a.m. Sunday as the miners were in the middle of their overnight shift.

Family members were spending a second night outside the pit, huddling near bonfires and wrapped in blankets to protect against the bitter cold. Some pitched tents, while others slept on small cots or upright in plastic chairs.

"The only thing we want is information and all they tell us is that they don't know," said a sobbing Yadira Gallegos, whose 28-year-old brother-in-law, Jesus Martinez, was just finishing his first week at the mine.

President Vicente Fox's chief spokesman, Ruben Aguilar, said Monday that the government "has a lot of hope that everyone will get out alive."

Robles said the roof of the mine was better reinforced after 400 meters, giving rescuers hope that they might be able to advance more quickly. He said if there were survivors, they could very well be trying to dig their way out from the other side.

Consuelo Aguilar, a spokeswoman for the National Miners' Union, said there had been concern over safety conditions in Grupo Mexico mines. She called for an investigation into the cause of the accident and the responsibility of company officials.

Rebolledo said safety conditions met Mexican government requirements as well as international standards "but accidents can always happen."

He said the union had raised no major disagreements over safety in annual meetings with the company. Mine administrator Ruben Escudero denied any company negligence, saying, "These mines can't operate if they don't meet the established minimum requirements."

Pedro Camarillo, a federal labor official unrelated to Olivia Camarillo, said officials found nothing unusual during a routine evaluation 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.

Coahuila's worst modern mining disaster occurred 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.