A suicide blast at a Shiite mosque in Islamabad killed at least 31 people on Friday, with 169 more wounded in the deadliest attack in Pakistan's capital since the 2008 Marriott hotel bombing.

City officials said 31 people died in the blast at the Imam Bargah Qasr-e-Khadijatul Kubra mosque in the Tarlai area on the city's outskirts, with scores more being treated for injuries. The death toll was expected to rise further.

A worshipper, Imran Mahmood, told AFP there was a gunfight between the bomber, a possible accomplice and volunteer security personnel at the mosque.

"The suicide attacker was trying to move forward, but one of our injured volunteers fired at him from behind, hitting him in the thigh," he told AFP.

He then "detonated the explosives", Mahmood, in his fifties, added.

No group immediately claimed responsibility, while Pakistani Prime Minister Shehbaz Sharif said those behind the blast would be found and brought to justice.

The attack was the deadliest in the Pakistani capital since September 2008, when 60 people were killed in a suicide truck bomb blast that destroyed part of the five-star Marriott hotel. (AFP)