According to Colombia Reports, the incident occurred at the San Patricio operation near Socha, outside of Bogota, at about 7 p.m. local time.

EFE identified the victims as Siervo Cristancho Machuca, Juan de Jesus Alfonzo Guenecio, Nelson Enrique Dueñas Valaguera and Jorge Humberto Mercado Valencia. Local officials said all have been recovered despite some areas of high inclination in the entries.

The met mine is owned by San Patricio Coal SAS and was initially opened in 2012.

The National Mining Agency released a statement confirming the suspension of mining operations at the complex and said that an investigation had commenced.

“Preliminary data showed that the emergency originated with a methane gas explosion,” agency Vice President Javier Garcia said.

Just three weeks ago, five other miners were killed in a similar incident in Samaca, which is also located in the Boyaca province. That operation has confirmed by local authorities to be legal; BBC reported that a probe is examining if the San Patricio operation is legally operating.