A suspected suicide attacker exploded a bomb near a Shia mosque in the northwestern Pakistani city of Peshawar late Saturday, killing at least 11 people, including the city police chief, and wounding 35, police said.

Most of the victims were police and municipal officials who were clearing the route for a procession of Shias in a crowded old quarter of the city, said police officer Aziz Khan. The procession had yet to begin.

This weekend marks the start of the festival of Ashoura, when Shias mourn the seventh-century death of the prophet Muhammad's grandson, Imam Hussein. In the past the festival has been a target for sectarian attacks.

The blast went off in a bazaar area about 180 metres from the mosque that was the starting point for the Shia procession. It caused a power outage that left the city centre in darkness, complicating rescue efforts.

At the bomb site, investigators found what appeared to be two legs from a suicide attacker, police officer Raza Khan said.

Eleven bodies and 35 wounded people were brought to Peshawar's Lady Reading Hospital, Aziz Khan said. The city's police chief, Malik Saab, was among the dead, said provincial police Chief Sharif Virk.

Hundreds of people crowded around the hospital seeking news of loved ones. By loudspeaker, hospital officials appealed for calm and blood donations.

Aziz Khan had been on duty near the mosque when the bomb went off.

"I thought my eardrums had burst. Then there were flames and the people were in panic. I remembered that there was a police contingent, so I went to see what had happened to my colleagues.

"Many were wounded in a bad way," he said.

There was no immediate claim of responsibility, but suspicion will likely fall on Sunni extremists.

Information Minister Mohammed Ali Durrani condemned the attack, saying it had been orchestrated by the "enemies of Pakistan, Islam and humanity."

Most Pakistani Shias and Sunnis co-exist peacefully, but militant groups on both sides are blamed for sectarian attacks that claim scores of lives every year.

Security is already high across Pakistan for Ashoura, amid fears that the sectarian violence in Iraq could stir up animosity between minority Shias and majority Sunnis in Pakistan.