A bomb has exploded in a mosque in the southern Pakistani city of Karachi killing at least 12 people, according to officials. More than 100 other people were hurt, 25 of them critically, said the chief medical officer at the main hospital. The mosque, in the business district, was full of Shia worshippers attending Friday prayer. Witnesses say ambulances have been ferrying casualties to hospital and the scene is one of carnage. An interior ministry official said the death toll might rise further. **Appeal for blood*** President Pervez Musharraf said the attack was a "heinous act of terrorism" and ordered an immediate investigation. A local government official told Reuters news agency more than 100 people had been inside the mosque at the time of the blast. A worker at a nearby brokerage house told the agency: "Our office on the 14th floor was shaken. We saw plumes of smoke, blood and bodies." Another witness, Kalb e-Abbas, told the Associated Press: "I was inside the mosque for Friday prayers when a bomb exploded. Something hit my arm and I saw blood all over my body." A state of emergency was declared at the main Civil Hospital where weeping relatives gathered amid scenes of chaos. Vehicles drove around making appeals for blood donations. Police cordoned off the mosque as angry locals besieged the area shouting abuse at officials and police officers. People from both Sunni and Shia communities chanted slogans and youths hurled rocks, damaging several official cars. **Famous building*** The explosion occurred at around 1300 local time (0800 GMT). No one has yet said they carried out the attack. Provincial government adviser Aftab Sheikh said many of the injured were in critical condition and several had lost limbs. "I condemn this attack; it was a barbaric act," he said. **PHOTO CAPTION*** A Pakistani police officer walks through the wreckage inside a mosque after a bomb ripped through during Friday prayer in Karachi. (AFP)