A powerful earthquake collapsed at least one coal mine and many flimsy mud houses in southwest Pakistan early Thursday, killing at least 20 people and injuring more than 200, an official said. The death toll was expected to rise even further as crews searched in the remote mountainous area, said Suhail Anwar Shaheen, the local deputy commissioner. At least four of the dead were killed when the coal mine in which they were working collapsed, said Shaheen, citing coal miners in the area. As many as 100 homes also collapsed, burying sleeping residents inside. The epicenter of the 5.9 magnitude quake was about 14 kilometers (8 miles) north-northeast of Harnai in Baluchistan province, according to the U.S. Geological Survey. The initial measurement of the quake’s strength was 5.7 magnitude. It struck about 20 kilometers (12 miles) below the Earth’s surface; shallower quakes tend to cause more damage. Read: What makes Haiti prone to devastating earthquakes The area, about 100 kilometers (60 miles) from Quetta, the provincial capital, is dotted with coal mines, which has Shaheen worried the death toll could rise. It struck in the early morning while scores of miners were already at work, he said. Most of the population in the area live in sunbaked mud houses, many of which collapsed. Rescue efforts were underway, but Shaheen said it would take hours just to reach many of the hardest-hit areas. Read: Haiti quake death toll rises to 1,419, injured now at 6,000 Local TV channels showed residents wrapped in blankets sitting on the side of the road waiting for the aftershocks to subside and help to arrive. The area is remote and already the autumn nighttime temperatures are chilly.