The police reported that at least eight people had frozen to death in their cars, while it was not immediately clear if others had died from asphyxiation after inhaling exhaust fumes in snow-bound vehicles.
Interior Minister Sheikh Rashid said the military had been mobilised to clear roads and rescue thousands still trapped near Murree, around 70km north-east of the capital, Islamabad.
Video shared on social media showed cars packed bumper-to-bumper, with 1m-high piles of snow on their roofs.
"The heavy snowfall caused a traffic jam and the closure of roads," Mr Babar Khan, a tourist who was stranded for hours, told AFP by phone."Roads were also closed due to falling trees in many places.
"The website of Pakistan’s National Weather Forecasting Centre said heavy snowfall was expected in the area until Sunday afternoon, while Information Minister Fawad Chaudry said "decades" of weather records had been broken in the last 48 hours.For days, Pakistan’s social media has been full of pictures and videos of people playing in the snow around Murree, a picturesque resort town built by the British in the 19th century as a sanatorium for its colonial troops.
The Punjab province Chief Minister’s Office said the surroundings had been declared a "disaster area" and urged people to stay away.
Prime Minister Imran Khan said he was shocked and upset at the tragedy.
"Unprecedented snowfall & rush of people proceeding without checking weather conditions caught district admin unprepared," he tweeted.
"Have ordered inquiry & putting in place strong regulation to ensure prevention of such tragedies."