Much of the fighting erupted in and around the old district of Lyari, long a focus of spats between rival gangs and a stronghold of President Asif Ali Zardari'a Pakistan People's Party (PPP).

A former PPP lawmaker was among the dead.

An official at the city's main government hospital put the death toll at 30 over the past 24 hours. Nineteen bodies had been brought in since Wednesday evening.

"Most of the killings have resulted from clashes between criminal gangs operating in Lyari and surrounding areas," a senior police official said.

A city of more than 18 million, Karachi has a long history of violence, and ethnic, religious and sectarian disputes and political rows can often explode into battles engulfing entire neighborhoods.