An apparent suicide bombing at a mosque in Pakistan's largest city, Karachi, has left at least eight worshippers dead and 50 injured.

Witnesses say the bomber mingled with Shi'ite Muslims crowding into the Karachi mosque for Friday prayers before blowing himself up.

The blast caused one of the building's beams to collapse. About 100 people were inside the mosque.

A protest developed at the scene, demanding the government do more to stop terrorist violence.

Provincial Interior Minister Aftab Sheikh says that the bomber appears to have entered the mosque despite the presence of police guards, and that better security measures will be needed in the future.

"Places of worship should be provided more security, and persons entering with bombs should be able to be detected," he said.

Friday's bombing follows an attack in March on a Shi'ite religious procession in the southeast city of Quetta that killed more than 50 people.

Pakistan's president, Pervez Musharraf, quickly condemned the attack, and police have begun an investigation.