The incident occurred at Cliffs Natural Resources’ Oak Grove longwall operation near Adger.

US Mine Safety and Health Administration spokeswoman Amy Louviere told ILN that a motor and mantrip came together on an S-curve underground.

“[It is] not known yet if both were moving or not,” she said.

Five contractors and one mine employee were involved, though no names have been released.

After being treated at the UAB Hospital in Birmingham, all were released. None had life-threatening injuries.

MSHA has begun an investigation, Louviere confirmed, but the operating status of Oak Grove mine, which is about 40km southeast of Birmingham, was not known at press time Monday.

Cliffs did not issue comment on the incident.

Oak Grove, which produces low-vol metallurgical coal and has been in operation since 1972, has a 2.5 million short ton annual capacity.