More than hundred bodies have been recovered from the site, according to the police.
"You find very few intact bodies. Basically, we are collecting bodies parts and putting them in bags," Bin Yameen, a senior police official, told Reuters.
"The chances of any survivors are very dim."
Pervez George, a civil aviation official, said the plane was about to land at the Islamabad airport when it lost contact with the control tower.
The Airbus A-321 belonged to the private Airblue airline.
Raheel Ahmed, a company spokesman, said the plane was carrying 144 passengers and six crew members.
"Basically, we are collecting bodies parts and putting them in bags."
Bin Yameen, police officer
"Apparently the cause of the crash is bad weather, but we leave that to the investigators," he told the AFP news agency.
"We are now preoccupied with rescue work and striving to take care of the relatives of the passengers who were on board."
A thick plume of smoke was seen rising from the forested hills.
The army said it was sending special troops to the area to help out along with
Al Jazeera's Kamal Hyder, reporting from Islamabad, said there had been heavy rain in the area in the morning.
"Visibility was very poor... Questions are now pointing at why the airplane would try and land considering weather conditions were so bad," he said.
"What will be critical is finding the black box which will give the final moments of the cockpit conversation that will give better clues into what happened."
The plane plummeted into a gorge between two hills and the distance to the nearest road was complicating the rescue operation.
"There is no village nearby and there is no ground link to the crash site. It took us one hour and 15 minutes to reach here from the nearest road, Aitbar Khattak, a rescue official, told state television.
Fakhar Ur Rehman, a correspondent of AAJ TV reporting from the scene, said rescue teams were heading to the scene on foot.
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The plane approaching Pakistan's Islamabad airport before came down in Magalla Hills
"They are climbing over the hills to reach the plane," he told Al Jazeera.
"The major issue now is how to get the bodies out of the rubble. There's smoke emitting from the debris and they're also trying to extinguish the fire."
The ED202 flight was headed from Karachi to Islamabad.
Hundreds of friends and relatives of those on board the flight gathered at the Islamabad airport seeking information.
"Nobody is guiding anyone. People are running from one counter to another," Arshad Mahmood, whose brother was on the flight, said.
"I'm praying for his survival, but I think there is little hope," Mahmood said.
Yousuf Raza Gilani, the prime minister, and the cabinet "expressed grief and sorrow over the tragic incident" and offered prayers for passengers who were killed.
"The federal cabinet declared one day national mourning because of this tragic incident. The prime minister called off the cabinet meeting until next week in the wake of this tragic incident," Gilani's office said in a statement.
Pakistan-based Airblue started operations in 2004 and is flying to many cities in Pakistan as well as five destinations in the Middle East and the UK.
The only previous recorded accident for Airblue was a tailstrike in 2008 at Quetta airport by one of the airline's Airbus 321 jets.
There were no casualties in that incident and damage was minimal, according to the US-based Aviation Safety Network.