ISLAMABAD, Aug. 13 (Xinhua) -- At least four laborers were killed and nine others injured in a coal mine explosion in Pakistan's southwest Balochistan province, local reports said on Monday.

According to the reports, the incident happened on Sunday night in Sanjawi area, some 30 km from Quetta, the provincial capital of Balochistan province.

The explosion was caused by the accumulation of poisonous gas in the mine, local media Abb Takk News said quoting rescue sources, adding the mine partially caved in following the explosion, trapping 15 miners who were working in the mine at the depth of 3,500 feet (1,050 meters) inside the debris.

Rescue teams later recovered four bodies and nine injured laborers from the rubbles. Rescue operation continued to recover the remaining trapped workers.

The injured miners were shifted to a nearby hospital where several of them are said to be in critical condition, said hospital sources.

Caretaker chief minister for Balochistan Alauddin Marri expressed deep grief and sorrow over the loss of precious lives in the incident. He has directed the concerned authorities to expedite the rescue operation and provide best medical treatment to the injured people.

Mining is considered highly dangerous in Pakistan where dozens of miners are killed each year due to the lack of up-to-date mining facilities, training and modern equipment.