Tensions flared as police began investigations into the blast which ripped through a Shia mosque in the city during Friday prayers.
The blast caused mayhem in Sialkot, 230km south east of the Pakistani capital, Islamabad, where Shia and Sunnis generally live in harmony.
Members of the Shia Imamia Students Organisation staged violent protests and burned tyres on Saturday after police blocked entry points to the city and Pakistani soldiers stepped up their patrols.
"We will continue our protest until the culprits behind the attack are arrested," the organisation's president, Nasir Shirazi, said.
Witnesses said vehicles were set alight and crowds attacked government buildings after thousands of people carrying black flags attended funeral prayers for nine of those killed in the mosque blast.
An angry crowd of about 2000 people carrying rifles, iron rods and batons ransacked the offices of Pakistan International Airlines, a branch of the state-owned National Bank, district courts and the district jail, the witnesses said.
The crowd torched the office of Sialkot's mayor and besieged a police station, with officers from a commando unit responding with gunfire and teargas to disperse them.
Security officials said earlier the mosque bomb blast, which also left dozens of people injured, was an act of terrorism.
"We believe the bomber carried the explosive into the mosque in a briefcase which he detonated while sitting amongst the worshippers and also blew himself up," the official, who did not wish to be named said.
Residents return to the mosque
where at least 30 people died
"It is an act of terrorism," police chief Nasar Ahmad said.
"We believe a suicide bomber carried out the dastardly attack at a time when hundreds of worshippers were present inside the mosque for Friday's prayers."
After the blast, experts defused a second 5kg briefcase bomb found outside the mosque, possibly saving many more lives, police said.
Nobody has claimed responsibility for the attack, but Pakistan has been plagued in recent years by sectarian violence between its Sunni majority and Shia minority.