A powerful bomb exploded inside a Shia mosque in Pakistan’s northwestern city of Peshawar on Friday, killing more than 30 worshippers and wounding dozens more, many of them critically.

The explosion occurred as worshippers had gathered in the Kucha Risaldar mosque in Peshawar’s old city area for Friday prayers.

Peshawar police chief Muhammed Ejaz Khan said the violence started when two armed attackers opened fire on police outside the mosque.

One assailant and one policeman were killed in the gunfight, and another policeman was wounded. The remaining attacker then entered the mosque and detonated a bomb.

Ambulances rushed through congested narrow streets and took the wounded to Lady Reading Hospital.

No group had immediately claimed responsibility.

More than 60 people were injured and the death toll may rise, said hospital spokesman Mohamed Asim.

“We are in a state of emergency and the injured are being shifted to the hospital. We are investigating the nature of the blast but it seemed to be a suicide attack,” police officer Mohammad Sajjad Khan said.

Rescue workers and volunteers gather at the site of bomb explosion in Peshawar
Rescue workers and volunteers gather at the site of the bomb explosion in Peshawar on Friday [Muhammad Sajjad/AP]

At least 150 worshippers were inside the mosque at the time of the explosion, said witnesses.

Similar attacks have occurred in Peshawar – 190km (120 miles) west of the capital, Islamabad – located near the border with neighbouring Afghanistan.

Shayan Haider, a witness, had been preparing to enter the mosque when the powerful explosion threw him to the street.

“I opened my eyes and there was dust and bodies everywhere,” he said.

At the Lady Reading Hospital’s emergency department, there was chaos as doctors struggled to move the many wounded into operation theatres.

“I saw a man firing at two policemen before he entered the mosque. Seconds later I heard a big bang,” said witness Zahid Khan.

Retired army officer Sher Ali who had been inside the mosque at the time of the explosion was injured by flying shrapnel. He made an impassioned plea to the Pakistani government for better protection of the country’s minority Shia Muslims.

“What is our sin? What have we done? Aren’t we citizens of this country?” he said from the emergency department, his white clothes splattered with blood.

Prime Minister Imran Khan condemned the bombing.

In recent months, Pakistan has experienced an increase in violence. Dozens of military personnel have been killed in scores of attacks on army outposts along the border with Afghanistan.