A coal mine gas blast in the town of Imelda in Zamboanga province, southern Philippines, caused the death of a worker and injured four others on 3 December.
The blast occurred inside a mine tunnel when workers were installing electrical lights.
Zamboanga Peninsula police director chief superintendent Angelo Sunglao said the workers in the mine noticed gas emissions entering from the tunnel before the blast.
Violation of safety regulations, including a lack of fire control equipment and required ventilation, have been cited as factors that triggered the disaster.
Small-scale workers have been conducting tunnelling work for coal in the area.
It has not been ascertained whether the mining work was unlawful or not.
The Philippine Zamboanga province has witnessed a number of mining disasters over the last 15 years.
In 2004, a coal tunnel collapsed in Diplahan town causing the death of six workers.
The biggest disaster in the province, however, occurred in 1995, when a coal mine tunnel in Malangas was destroyed by a massive methane gas explosion, which killed more than 100 people.