ISLAMABAD, April 10 (Xinhua) -- At least four laborers were killed and two others injured in an explosion in a coal mine in Pakistan's northwest Khyber Pakhtunkhwa province on Wednesday, local media said.

According to reports, the explosion was caused by the accumulation of poisonous gas in the mine located in Darra Adam Khel town of the province.

As a result of the blast, a portion of the mine caved in, trapping the miners who were digging coal inside the mine, said local Urdu TV channel Dunya News.

Following the incident, police and rescue teams reached the site and recovered four bodies and two injured laborers from the rubble.

The injured miners were shifted to a nearby hospital where one of them was said to be in critical condition.

According to the Pakistan Central Mines Labor Federation, about 100 to 200 laborers were killed or injured in coal mine accidents across the country every year.