A man removes his pushcart from the rubble of a damaged house in Harnai, Balochistan, Pakistan. Reuters

At least 23 people were killed and about 300 injured when a 5.7 magnitude earthquake struck southwestern Pakistan in the early hours of Thursday, with rescuers trying to reach coal miners reportedly trapped underground, the Disaster Management Authority said.

The death tally was expected to rise even further as crews searched in the remote mountainous area, said Suhail Anwar Shaheen, the local deputy commissioner.

Rescue workers said most of those killed were women and children. The most serious cases were being sent by ambulance to Quetta.

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The earthquake struck at the relatively shallow depth of 20km (12 miles) with an epicentre 102 km (62 miles) east of the city of Quetta, the US Geological Survey (USGS) said.

People gather outside a hospital following an earthquake in Harnai, Balochistan, Pakistan, on Thursday. Reuters

It was felt across at least six cities and towns, but the worst-affected area was the remote mountainous district of Harnai, where landslides triggered by the jolt blocked some roads, hampering rescue efforts.

Authorities are also contending with phone and electricity outages after pylons were damaged.

"We are receiving information that 20 people have been killed due to the earthquake," said Balochistan's home minister Mir Zia ullah Langau, adding that 100 people were injured.

Local residents gather outside their houses after an earthquake hit the area in Quetta, Pakistan, on Thursday. AP

More than 100 mud houses collapsed and many buildings were damaged. Television footage showed buildings with gaping cracks, caved in roofs and crumpled walls.

"The earthquake struck at around 3am. The seriously injured people are in hospital and they are waiting for ambulances to be moved to Quetta," said resident Muzaffar Khan Tareen.

Pakistan straddles the boundary where the Indian and Eurasian tectonic plates meet, making the country susceptible to earthquakes.