At least 20 people were killed in a suicide attack on religious procession of Shia Muslims in the south Pakistani city of Karachi on Monday, a provincial minister said.

Sagheer Ahmed, health minister in Sindh province, of which Karachi is the capital, confirmed that 20 people were killed in the attack. He said that up to 30 other people were injured.

Hospital sources said that up to 50 people were injured, who were shifted to different hospitals of the city. The provincial government declared emergency in hospitals.

Police said some unknown militants also exchanged fires with the security forces after the powerful bomb blast occurred in a main Muharram procession in connection with the Yaum-e-Ashura, on MA Jinnah Road of the commercial hub.

It is reported that more than 15 vehicles were set ablaze in different parts and some were seriously damaged.

Television pictures showed a big cloud of smoke over the scene and television reporters said angry worshippers attacked media vehicles and police mobiles.

The Shia march was taken out of Nishtar Park and was on way to head to the final destination. The organizers decided to continue the procession despite the blast. They appealed to the mourners to be peaceful.

Pakistani Prime Minister Yousuf Raza Gilani strongly condemned the blast at main procession and ordered immediate inquiry and submission of report. He also ordered for provision of immediate best medical facilities to the injured.

It is the third bomb blast in Karachi in three days. Scores of peoples were injured in the two blasts on Saturday and Sunday, according to the police.

Karachi Mayor Mustafa Kamal asked the citizens to remain peaceful and do not show any reaction. He expressed shock over attacks on property and vehicles after the blast. He said that the blast was aimed at destroying peace of the city.

During the first Muslim month of Muharram, Shiites across the world mourn the death of the Prophet Mohammad's grandson Imam Hussain in the Iraqi city of Kerbala in the year 680.

Pakistan's security forces have been on high alert as Muslims are marking the holy day of Ashura, the Shia calendar's biggest event.

On Sunday evening at least 15 people, including mourners and policemen, were killed and over 100 injured when a suicide bomber ripped through a Muharram procession near a Shia mosque in the Pakistan-controlled Kashmir.