A blast has hit a Shia Muslim religious procession, killing 18 people and wounding 20 others, in Pakistan's central Punjab province, local police say.

The explosion hit the gathering in Rahim Yar Khan district where Shias were marking the 40th day of mourning of the death of the Prophet Mohammad's grandson Imam Hussain, Al Jazeera’s Zein Basravi reported from Islamabad.

“Local police tell us that a bomb was planted in the path of the planned procession. As people began leaving the mosque, the bomb went off, killing and injuring so many people,” our correspondent said.

“As the injured were taken to the hospital, the survivors and mourners left behind, angry at the apparent lack of security, turned on the police. They began throwing rocks. And ironically, the police had to subdue the victims by firing teargas into the crowd."

The processions of Shia Muslims, who make up about 20 per cent of Pakistan's population, are often attacked by armed Sunni Muslim groups who consider them apostates of Islam.

Source: Al Jazeera and agencies