At least 40 people have been killed by a huge blast in a Pakistan province where hundreds of members of a conservative political party were gathered.

More than 130 others were injured in the suspected bomb attack, and the sheer number of victims has placed huge stress on the local hospitals.

A health emergency was declared as blast victims were rushed to medical facilities that were struggling to cope.

Pakistan’s Prime Minister Shehbaz Sharif vowed to punish the “terrorists” responsible and “eliminate them from the face of existence”.

The blast took place at a gathering of the conservative Jamiat Ulema Islam-Fazl (JUI-F) party in the northwestern Khyber Pakhtunkhwa province.

The party is known for its links to hardline political Islam in the former tribal area of Bajaur, which borders Afghanistan.

The provincial police chief Akhtar Hayat told Reuters the explosion was caused by a suicide bomb.

An emergency was declared in the hospitals of Bajaur and adjoining areas where most of the injured were taken, district police officer Nazir Khan said.

The critically injured were transported from Bajaur to hospitals in the provincial capital Peshawar by military helicopters.

“The JUI-F organised a workers convention in Khar town of Bajaur in which 40 people lost their lives and more than 130 were injured,” Khan said.

Pakistan has had a resurgence of attacks by Islamist militants since last year when a ceasefire between the Tehreek-e-Taliban Pakistan (TTP) and officials in Islamabad broke down.

However, most of the recent attacks have been on security forces and installations, rather than political gatherings.

The TTP pledges allegiance to, but is not directly a part of, the Taliban in western neighbour Afghanistan.

Pakistan’s security forces say the TTP have sanctuaries in Afghanistan, which the Taliban run-administration there denies.

Afghanistan’s administration condemned the explosion in a statement by their spokesman Zabihullah Mujahid.

The TTP are not the only militant group to carry out attacks in the area, which has also been hit by a local chapter of the Islamic State.

The targeted party, the JUI-F, is a major ally of the coalition government of Prime Minister Shehbaz Sharif, which is preparing for general elections to be held by November.