At least 20 people were killed and more than 200 injured when an earthquake struck southern Pakistan, Disaster Management Authority Director General Naseer Nasir said on Thursday.

The earthquake with a magnitude of 5.7 struck in the early hours of Thursday while people were sleeping. Rescue workers said the dead were mostly women and children.

The quake was relatively shallow at 20 kms (12 miles) with an epicentre 102 km (62 miles) east of Quetta, said the U.S. Geological Survey (USGS).

More than 100 mud houses collapsed and a large number were damaged, including government buildings. Hundreds of people were rendered homeless, Sohail Anwar, deputy commissioner in the city of Harnai, told Reuters.

Social media showed houses shaking and light fittings swaying as the quake struck, and later stunned residents gathering in the street in the dark.

The injured were rushed to hospital, while some were treated on stretchers in the street under phone torch light.

A 7.7-magnitude earthquake hit Quetta in 1935, killing between 30,000 and 60,000 people, making it one of the deadliest quakes to hit South Asia in recorded history.