QUETTA, Pakistan -- Around 20 people have been after a 5.7 magnitude earthquake hit southern Pakistan in darkness early on Thursday, government officials said.

Many of the victims died when roofs and walls collapsed, Suhail Anwar Hashmi, a senior provincial government official, told AFP.

A woman and six children were among twenty dead, he said. "We are receiving information that 20 people have been killed due to the earthquake. Rescue efforts are under way," provincial interior minister Mir Zia ullah Langau added.

Naseer Nasar, the head of Balochistan's Provincial Disaster Management authority, told AFP that between 15 and 20 people had died, but that the toll may increase. The worst-affected area was the remote mountainous city of Harnai, in Balochistan, where a lack of paved roads, electricity and mobile phone coverage has hampered the rescue effort.

The earthquake was also felt in Balochistan's provincial capital Quetta.

The US Geological Survey said the quake had a magnitude of 5.7 and struck around 3am at a depth of around 20 kilometres (12 miles). Pakistan straddles the boundary where the Indian and Eurasian tectonic plates meet, making the country susceptible to earthquakes.

In October 2015, a 7.5-magnitude quake in Pakistan and Afghanistan killed almost 400 people across rugged terrain that impeded relief efforts.

The country was also hit by a 7.6-magnitude quake on October 8, 2005, that killed more than 73,000 people and left about 3.5 million homeless, mainly in Pakistan-controlled Kashmir.