Fifty-five people were killed, and scores injured when a powerful blast ripped through a stage erected in a park where Pakistani religious leaders and hundreds of faithful were offering evening prayers on the occasion on Prophet Mohammed's birth anniversary.

The bomb, planted under a stage erected in the crowded Nishtar Park in Pakistan's port city Karachi, tore through scattering bodies dressed in ceremonial white outfits across the area.

While 51 deaths were confirmed by officials in Karachi, television channels reported that 55 were killed in the explosion.

Those killed in the bomb attack included head of the Islamic group Tehrik Awam Ahli-Sunnat Haji Hanif Bilo and his son Hafiz Bilo.

TAAS organised today's congregation at the park in Karachi. The condition of number of TAAS leaders who were injured in the blast was stated to be serious.

Local Geo TV reported said some of the leaders of the banned Sunni outfit, Sunni Tehrik, who took part in the meeting, were injured in the explosion. A number of television journalists were also injured in the attack.

"Human remains are scattered all over the place. The injured are being rushed to local hospitals. It was a powerful bomb blast and we fear a very high casualty list," a spokesman of the local administration said.

Nearly 125 injured have been shifted to nearby hospitals and the condition of most of them was said to be serious. Emergency has been declared in hospitals. 

"We fear a very high casualty list," a spokesman of the local administration said.

Interior Minister Aftab Sherpao told reporters in Islamabad that police were not sure if it was a suicide attack.

Chief Secretary of Sindh province Fazalur Rehman denied that the blast occurred due to a security breach while Sindh Interior Minister Rauf Siddique feared a suicide attack and said the area has been put under high security alert.

The stage was totally destroyed in the blast.

Sherpao and top police officials declined to speculate who could be behind the blast. Karachi, Pakistan's biggest city housing over 12 million people has been witnessing sectarian strife for over a decade with extremist groups of Sunnis and Shias targeting each other's religious congregations.

"We have not received any reports that it was a suicide attack. Security has been tightened in the city and an emergency has been declared. Investigation has been ordered and the probe will be made public," Sherpao said in Islamabad.

Soon after the blast, a mob pelted stones at the police and paramilitary rangers when they arrived at the site.

Police then fired in the air to disperse the crowd.

President Pervez Musharraf [Images] and Prime Minister Shaukat Aziz strongly condemned the "heinous act" and ordered security to be stepped up at mosques, a government statement said.

Chief Minister of Sindh Province Arbab Rahim has announced Rs 1,00,000 compensation for those killed in the blast and Rs 50,000 for those injured.

Sindh province's party Motahida Qaumi Movement has announced a three-day mourning.

Just a couple of days ago, 31 women and children were killed and more than 50 others injured in a stampede during an religious gathering.