Iftikhar Babar, the police chief in the central city of Multan, told Reuters on Monday: "Everyone is dead. I am standing at the site."
Hasan Jaferry, a PIA spokesman, said flight PK 688, on its way to Lahore before flying on to Islamabad, crashed 10 minutes after take-off from Multan airport. It was carrying 41 passengers and four crew.
Among the passengers were two Pakistani army officers and two judges, Aljazeera's correspondent reported.
One witness told Reuters: "Bodies are badly charred. The debris has caught fire."
He said rescue workers from the privately run relief foundation Edhi, the Civil Aviation Authority and the army were taking part in the rescue operation.
The Fokker aircraft crashed near a government primary school, about 3km from the airport.
Mohammad Akram, a farmer who was working in his fields, said: "I saw the plane diving downwards. It hit electricity wires and then crashed after hitting a wall of an orchard. All of a sudden it caught fire."