The US Geological Survey website said a magnitude 6.4 earthquake struck 60 kilometres north-east of Quetta, the capital of Balochistan, at 5:10 am (2310 GMT). It lasted about 40 seconds.
With the earthquake hitting just before sunrise, people fled their houses in panic. Television footage showed terrified families wrapped in blankets sitting by the roadsides in Quetta.
"We have confirmation of more than 170 deaths in various villages and more than 400 are injured," said Dilawar Khan Kakar, mayor of the most severely hit district of Ziarat, located some 50 kilometres north-east of Quetta.
According to Kakar, almost every single house was destroyed in Wam village, home to more than 200 families.
His deputy, Momin Khan Dummar, feared that the death toll could be as high as 190.
However, Farooq Ahmed Khan, chairman of the National Disaster Management Authority (NDMA), confirmed only 115 deaths and around 300 injured.
"The death toll is feared to rise. We will have an exact figure later in the day," he told reporters in Islamabad.
He said eight villages, mostly consisting of mud houses, were hard hit by the strong tremor. He added that the government has initially established two tent villages in Ziarat for the 2,000 to 2,500 people estimated to have lost their homes.
At least 10 people were killed in other districts, news reports said.
Pakistan Meteorological Department Director General Qamaruz Zaman Chaudhry described the tremor as a shallow earthquake, at a depth of about 10 kilometres.
"A shallow earthquake of this magnitude is normally very destructive," he said.
Officials were trying to assess the extent of the devastation in Balochistan, Pakistan's largest, but most sparsely populated, province.
Relief workers had only reached villages near main roads. Remote areas remained inaccessible.
The earthquake also triggered mudslides that blocked roads and hampered relief work. Twelve military helicopters were flown to the area, while 400 paramilitary troops were taking part in the relief efforts.
Locals buried 75 people in a mass grave in Wam village.
Dozens of severely injured people were moved to various hospitals in Quetta from Ziarat, where Pakistan army had set up a field hospital.
Later in the day, severe aftershocks caused panic in Balochistan. The strongest aftershock, measuring 6.2 on the Richter scale, hit the province at 5:32 pm (1132 GMT), according to the US Geological Survey.
In Quetta, horrified people ran towards open areas, stumbling upon each other and sustaining more injuries, the Urdu-language Geo news channel reported.
"More than 25 people have been moved to the hospital. Some of them came here with broken arms and legs. They had jumped from the first or second floor of the building," a medical officer said.
The NDMA chairman said the authorities were asking people in quake-affected areas not to spend the night in damaged houses. "These aftershocks can demolish damaged mud houses," Khan said.
The European Union, Germany and India offered humanitarian assistance for the quake victims.
Pakistan said it would welcome the aid but had no intentions to formally seek international help.
"According to initial information the situation is localized so far. We can deal with it," Khan said.
Balochistan was also struck by a magnitude 7.3 earthquake in 1997 which killed more than 100 people. The worst earthquake hit the province in 1935, killing more than 30,000 people and almost flattening the entire city of Quetta.
On October 8, 2005, a massive earthquake measuring 7.6 on the Richter scale shook Kashmir and Pakistan's mountain region, killing at least 73,000 people and leaving 3.5 million others homeless. dpa ns yam fi ff im pw ncs
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