Initial reports suggested the collapse was caused by flooding at the mine in the municipality of Muzquiz, in the northern state of Coahuila.
The body of one miner has been found at a small coal mine in a northern Mexico border state that flooded and collapsed, leaving six miners still missing.
There had been complaints for years about unsafe conditions at mines in the area.
The federal civil defence office said one miner's body had been found and the search was continuing for the other six in the coal belt of the northern state of Coahuila.
The Coahuila Labour Department said the mine was apparently hit by some sort of collapse and flooding. President Andres Manuel Lopez Obrador said a dam or holding pond had collapsed, causing the flood.
Efforts have concentrated on pumping water out of the mine. The army dispatched a 28-member team that specialises in looking for victims in collapsed structures and it was using two trained dogs at the mine.
The Micaran mine, located in Muzquiz township, appears to be a type of deep, narrow, open pit with steep earth walls, with at least one tunnel at the bottom burrowing into the coal face. The area is about is 130 kilometres southwest of Eagle Pass, Texas.
Violation of safety codes
Coal mines in the area have been hit by deadly accidents in the past.
An accident on February 19, 2006, in the Pasta de Conchos mine in nearby Sabinas, Coahuila, killed 65 miners, but only two bodies were recovered.
Mexican authorities called off that search and closed the mine five days after the accident, arguing that it was unsafe due to toxic gas.
The Miguel Agustin Pro Human Rights Center published a letter from families of the miners killed in the Pasta de Conchos disaster, saying that coal mines in the area routinely violated safety codes.
The relatives' group has reviewed conditions at a large number of mines since 2006 and reported that about 100 miners have died in mishaps since the Pasta de Conchos accident.
In recent mine inspections, they said, they had found miners working in sneakers with no safety equipment, drinking water or gas monitors.
“The rule continues to be that these mines operate in deplorable conditions,” the group wrote. “For decades, the mines have been allowed to operate with complying with the laws.”
Many of Coahuila's small-scale mines are astonishingly primitive; rough logs are used to shore up tunnels and miners descend atop crude coal buckets on cables pulled by car engines.
The issue is a key one for Lopez Obrador, who has promised to get justice for miners' families, while simultaneously increasing the amount of coal the government purchases to burn in power plants.
Lopez Obrador wrote in his social media accounts that federal forces were aiding in the effort and said, “We hope the rescue will be positive for the relatives, and for everyone.”