Four miners were killed on Tuesday after inhaling poisonous gas in a coal mine in Balochistan's Duki area, the province's Mines and Minerals Chief Inspector Abdul Ghani said.

The workers, who had entered the mine in Chamalang in the afternoon, died of suffocation after inhaling the poisonous gas, he said, adding that their bodies were retrieved from the mine in a rescue operation.

The bodies were transferred to a nearby hospital and will be handed over to the relatives of the deceased after completing formalities, Ghani said. All four miners hailed from Balochistan's Zhob district, the official further said.

Pakistan Central Mines Labour Federation Secretary General Sultan Khan told Dawn.com that fatal incidents were increasing because of a lack of implementation of laws related to mines.

As many as 90 people have been killed in incidents in different mines across Balochistan this year, he added.

Coal mining has historically been fraught with hazards, which are similar to those associated with the aftermath of natural disasters: suffocation, gas poisoning, roof collapse, rock burst, gas explosions and a plethora of lung diseases, including incurable diseases like coal worker's pneumoconiosis, also known as black lung disease.

Earlier this year, eight coal miners suffered serious burn injuries in an explosion inside a mine in Duki.

In March, 13 miners were killed in two separate incidents within the span of a week.

Seven miners were killed in a blast at a coal mine in Harnai which was caused by a build-up of methane gas.

Earlier that week, six workers were found dead after they were trapped inside a coal mine in Bolan district that collapsed following a methane gas explosion the previous day.