At least 31 people have been killed and more than 30 injured in a suicide blast outside a polling station in Quetta's Eastern Bypass area on Wednesday, officials said.

Police officials and civilians both are among the dead. Eight of the wounded are in critical condition.

A statement issued by Quetta police said a suicide bomber blew himself up after he was stopped from entering the Tameer-i-Nau Education Complex school, which is serving as a polling station. Earlier reports had said the target of the blast was a police van.

“(The bomber) was trying to enter the polling station. When police tried to stop him he blew himself up,” a local administration official in Quetta, Hashim Ghilzai, told AFP. Police officials rushed to the site and launched a probe into the blast.

The explosion occurred outside the school in Quetta's 'sensitive' NA-260 constituency where polling was taking place. A number of target killing incidents and bombings have taken place in this area over the last 15 years.

The blast has left 31 people dead and more than two dozen people injured, Deputy Inspector General (DIG) CTD Aitzaz Ahmed Goraya said quoting the latest figures.

A station house officer (SHO) injured in the attack is in a critical condition, DawnNewsTV reported. An emergency has been imposed at the Civil Hospital.

Polling was halted at the school after the blast, but it resumed after a few hours.

Volunteers and security officers visit the site of a bombing in Quetta. —AP

The attack was claimed by the militant Islamic State (IS) group through its official Amaq news agency.

The blast is the first major terror incident to have occurred since polling kicked off across the country for 2018 general elections.

Earlier in the day, unidentified assailants hurled a hand grenade at a polling station in the village of Koshk, in Khuzdar district. The attack left one policeman dead and three wounded.

Balochistan has suffered the brunt of a series of attacks that killed more than 180 people across Pakistan during the brief but acrimonious election campaign, including a blast in Mastung district also claimed by IS which killed 153 people, including local politician Siraj Raisani.

He was one of three election candidates killed by militant attacks during the election campaign.

The military has stationed over 370,000 personnel across the country to ensure security for the election, bolstered by an additional 450,000 police.