SHAFAQNA (Shia International News Association) -- The victim's body was then set alight, according to witnesses.
The unnamed victim had earlier been handed over to the police after burnt pages of the Koran were found in a mosque in Dadu district, 330km (200 miles) north of Karachi, where he had been staying overnight.
Hours later a mob went to the police station, seized the man and killed him.
The district police chief, Usman Ghani, told the BBC the gruesome incident was filmed on mobile phones. He said the footage was being reviewed to identify culprits.
The case of Rimsha Masih, a young Christian, caused an outcry
Thirty people have so far been detained in connection with the attack.
The local police chief and five of his officers have been arrested for failing to protect the man.
The BBC's Shahzeb Jillani says blasphemy is a highly sensitive issue in Pakistan, where scores of people have been killed by mobs or vigilantes.
Our correspondent in Karachi adds that the controversial laws are often misused to persecute minorities or settle scores.
Most recently, international attention focused on the case of Christian teenager Rimsha Masih, who was held over blasphemy allegations.
The case was dismissed last month after a neighbour gave evidence that she had been framed, possibly to chase Christians out of her neighbourhood outside Islamabad.
In 2011, two leading politicians - the Governor of Punjab province, Salman Taseer, and the Religious Minorities Minister, Shahbaz Bhatti - were assassinated after speaking out against the existing blasphemy legislation.