"There will be a lot of people still stuck under the rubble and it is getting dark here ... which will hamper [relief] efforts, so we may well see the death toll rise," he said.
Khan reported that locals were scared to stay in their homes because of fears of aftershocks and many people were trying to leave the area.
"Roads out of Ziarat [the epicentre] are packed. It is a chaotic scene down there."
Khan said that the government is not asking for international assistance.
About 12 hours after the initial earthquake an aftershock of 6.2 magnitude rocked the region, but there were no immediate reports of additional casualties or damage.
Troops and helicopters
A Pakistani military spokesman said about 250 troops and two helicopters had been sent to Ziarat from Quetta, while an aerial assessment of the damage was also under way.
|People fled their homes after the first quake hit Baluchistan province before dawn [AFP]
"The destruction is heavy, people need immediate help and we are providing assistance to the affected people," Colonel Mohammed Babar said.
Retired Lieutenant-General Faruq Ahmed, chairman of the National Disaster Management Authority, said tents, blankets and food had been sent to the area along with medical teams to treat the injured.
Maulvi Abdul Samad Akhunzada, a provincial minister, said: "Around 15,000 people have been affected, 1,500 houses have collapsed. More than 150 people have been killed and countless are injured."
"We require tents, items of food and medicines. Teams of doctors should also be dispatched immediately."
Dilawar Khan, chief of the Ziarat district, said that hundreds of mud houses had collapsed, while further damage was reported in neighbouring Pishin district.
Khan said that some houses had been buried in a landslide triggered by the earthquake.
"Rescue work is being carried out by the villagers themselves, but a larger operation is needed here," he said.
A reporter for Associated Press news agency saw dozens of bodies and injured in a hospital in Kawas in Ziarat district. Mohammed Irfan, a doctor, said the hospital was unable to cope with the number of injured it was receiving.
Sohail-ur-Rehman, another provincial official, said that the authorities were rushing to help about 15,000 homeless people and to bury the dead.
"Graves are being dug with excavators as we can't keep dead bodies in the open," he said.
Sanaullah, a resident, told the Associated Press news agency: "When the earthquake occurred, I was sleeping in my building with my children and suddenly I heard a noise and I recognised it was an earthquake.
"I ran to get my children. The window broke and my hand was injured and now I am waiting with my children on the roadside."
The earthquake took place at the shallow depth of 10km and hit about 70km northeast of Quetta, the US Geographical Survey said.
The Pakistani Meteorological Department said that two quakes had struck before dawn, the second of which was larger than the first.
Al Jazeera's Kamal Hyder, reporting from the Pakistani capital, Islamabad, said: "The first quake struck at 4.35am [22:35 GMT on Tuesday] forcing people out onto the streets, and then at about 5.10am the stronger second quake, measuring 6.5 on the Richter scale, is said to have hit."
Hyder said that Quetta, however, had largely escaped extensive damage.
But Imran Khan reported: "In Quetta we are seeing a ghost town. Normally this place would be buzzing, the shops would be open, people would be in restaurants ... but people are scared of going inside buildings."
Quetta was largely destroyed and about 30,000 people were killed in a severe earthquake in 1935.
The region's worst earthquake was in October 2005 when about 75,000 people were killed, most of them in mountainous northern Pakistan, in a 7.6 magnitude quake.