* Quake of magnitude 5.7 struck east of Quetta city

* More than 100 houses collapsed

* Most victims were women and children, say rescue workers

* Prime Minister orders emergency assistance

The earthquake struck at a shallow depth of about 20 km (12 miles), with its epicentre 102 km (62 miles) east of the city of Quetta, the U.S. Geological Survey (USGS) said.

“I was sleeping when suddenly my entire house jolted,” Munir Shah, 40, a resident of Harnai district in Balochistan province, told Reuters by telephone.

“I took my children and wife outside. It was a terrifying situation as houses in Harnai were collapsing, my house was also damaged,” he added.

“I found a large number of people under debris. Some of them might have died.”

More than 100 mud houses collapsed and many buildings were damaged, said district official Sohail Anwar. Television images showed buildings with gaping cracks, caved-in roofs and crumpled walls.

About 250 homes collapsed and many people were killed by falling roofs and crumbling walls in the district’s Babu Mohallah neighbourhood, said Nawab Khan, a local journalist.

“The entire town is a picture of devastation, as no house looks safe, thousands of people are rendered homeless and are under open sky,” Khan said, adding that almost 70% of power supply to the district had been disrupted.

Prime Minister Imran Khan ordered immediate assessment of the damages and offered condolences to families that lost loved ones, adding, “I have ordered immediate assistance on an emergency basis … for the earthquake victims.”

Social media showed houses shaking and light fittings swaying as the quake struck. Stunned residents later gathered in the streets in the dark. Geo Television carried CCTV footage of trucks shaking.

Rescuers sifted rubble for survivors, with some of the injured being treated on stretchers in the street by torchlight from mobile telephones.

“The earthquake struck at about 3 a.m.,” said one resident, Muzaffar Khan Tareen, adding that some of the seriously injured were in hospital awaiting ambulances to take them to Quetta.

An army helicopter flew at least nine of the seriously injured to Quetta, state-run Associated Press Pakistan said.

Aftershocks were being felt across the region. Pakistan sits on top of colliding tectonic plates and earthquakes are common.

A quake of 7.7 magnitude that hit Quetta in 1935 killed between 30,000 and 60,000 and destroying much of the city.

In 2005, an earthquake of magnitude 7.6 killed about 73,000 people when it struck about 95 km (59 miles) northeast of the capital, Islamabad.

(Reporting by Bhargav Acharya in Bengaluru and Gul Yousafzai from Quetta; Writing by Michael Perry; Editing by Stephen Coates and Clarence Fernandez)