Time is running out for 65 Mexican workers who are trapped underground after a blast in a coal mine in the northern state of Coahuila.
Anxious relatives continue to wait for news of loved ones
Using picks, shovels and their hands, rescue teams have got closer to the miners, but they said they still did not know if the men were alive.
The workers were carrying limited supplies of oxygen when the blast happened on Sunday.
Relatives have camped outside the mine for three days waiting for any news.
Officials have said that prospects were slim but there was still a chance of finding survivors.
With methane gas still in the mine, the searchers are not using mechanical equipment for fear of new explosions.
Late on Tuesday, rescuers said they were within 50m (yards) of where some miners were working when the explosion occurred at 0230 local time (0830 GMT) on Sunday.
But most of the workers are thought to be trapped in tunnels at least 2km (1.25 miles) into the mine.
Experts from the US are expected to join the rescue effort on Wednesday afternoon.
Ten miners who were underground escaped safely, and another 12 were rescued, suffering from burns and broken bones.
The owners of the mine, Grupo Mexico, have denied workers' claims that safety procedures were not followed.
The mine passed a labour ministry safety check only two weeks ago, a mine official said.
The explosion is thought to have been caused by gases igniting.
State Governor Humberto Moreira Valdes is overseeing the rescue operation at the mine, which lies near the town of San Juan de Sabinas, 100km (60 miles) from the US border.
The miners' oxygen tanks are designed to last for six hours, and have almost certainly run out.
"There is always hope," said Juan Rebolledo of Grupo Mexico. "There could be pockets of air down there."
But Edgar Hernandez, an engineer whose brother Jose is missing, told Reuters news agency: "We are desperate and thinking the worst.
"The rescue is going very slowly and down there they have no oxygen, no light, no food."
Juanita Carrera, 28, whose husband Margarito is one of those trapped in the mine, said: "Why don't they go faster?"
Norma Vitela, who heard on the radio that her husband was also trapped underground, said: "We are waiting for a miracle from God."
The coal mine is located in a remote and semi-desert region in Coahuila - Mexico's top mining state. About 95% of the country's coal reserves are located there.
Grupo Mexico is the world's third-largest copper mining firm, and also mines other mineral deposits.
Some workers have criticised the mining company
A spokeswoman for the National Miners' Union, Consuelo Aguilar, said there had been concern over safety conditions in Grupo Mexico mines and called for an investigation to determine the exact cause of the accident.
But Pedro Camarillo, a federal labour official, told reporters that nothing unusual was found during this month's routine inspection.
There have been a number of fatal mining accidents in Coahuila state. The worst was in 1969, when more than 153 miners were killed in a pit at the village of Barroteran.
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