Rescue crews in Mexico have been working nonstop to reach 65 miners who have been trapped after an explosion in a remote coal mine in northern Mexico.

The blast occurred early Sunday at a mine in Coahuila state near the U.S. border. Officials with Grupo Mexico, the company that owns the mine, say a gas buildup triggered the explosion.

The miners are trapped about three kilometers underground from the mine's entrance. Officials say the miners carried only enough oxygen to last six hours. The director of Coahuila's emergency services (Sergio Robles) says rescue efforts have been hampered by toxic gas in the mine.

At least seven miners working near the mine's entrance were injured in the blast, and were taken to a local hospital.

Some information for this report was provided by AP and Reuters.