An Ashura procession in Quetta on Tuesday was attacked by gunmen and a suicide bomber, triggering chaotic shoot-outs and mob rampages, left almost 50 Shia dead and 150 injured.
"Two gunmen on top of a building opened indiscriminate fire at the same time as a suicide bomber walked into the crowd and blew himself up. Another two gunmen accompanying the bomber on the ground then sprayed bullets into the crowd," a Quetta-based intelligence official, who could not be named, told AFP.
"Police then joined in the firing, not knowing where the shots came from they started firing in all directions, up and down.
"This led to complete chaos and pandemonium. It was a free-for all."
Most of the Quetta victims were shot in the cross-fire, the intelligence official said.
Three of the four gunmen were shot dead while the other was wounded by a bullet in his head. He survived and is under arrest.
As authorities began an inquiry, helicopters flew overhead and troops patrolled the deserted streets of Quetta, while Shia gathered for mass funerals.
Burials were delayed as the Shia community demanded the release of about two dozen of its members detained when they went to hospitals to donate blood, community leaders said.
Schools, colleges and shops remained closed under the second day of curfew ordered by mayor Mohammad Rahim Kakar.
Up to 70 shops, mostly owned by Sunni merchants, were torched by mobs on Tuesday along with a dozen vehicles.
President Pervez Musharraf condemned the violence as a "terrorist attack" and ordered an inquiry.
Interior Minister Faisal Saleh Hayat blamed "misguided extremists."
"They want to create chaos. The government is aware of their designs and determined to continue its fight against extremism and sectarianism".