Rescue workers had not heard from the workers since the 8am explosion and warned the miners may all be dead unless they were trapped in a pocket with breathable air.

High methane levels prevented rescuers from entering the mine after the accident for much of the day, which occurred around 8 a.m., the mayor of the municipality of Sabinas, Jesus Montemayor, told Mexican radio.

"The explosion was very strong. If it was deep inside the rescue will be more difficult ... there's a lot of despair but we have to wait until the methane gas level allows us to start the rescue."

The mine appeared to be one of the many small-scale, artisanal coal mines that dot the landscape in Mexico's Coahuila state near the Texas border rather than a modern, mechanized facility.

Reuters