The train was heading from the eastern city of Lahore to the south-western province of Balochistan when the accident occurred before dawn.
The death toll may rise as three injured people were in a critical condition and other passengers could still be trapped inside damaged carriages, a police official, Hafeez Bugti, said.
Rescuers were cutting through the carriages with electric cutting tools to reach trapped passengers, Bugti added.
Train accidents are common in Pakistan where many tracks laid by the British rulers during colonial times before 1947 have not been upgraded since.
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