Security officials examine the site of a blast at a religious school in Peshawar on Tuesday. Abdul Majeed/AFP

At least eight students were killed and scores more wounded on Tuesday in a bomb attack on a Koran study class at a religious school in northwestern Pakistan, officials said.

More than 60 people had been taking a lesson when the explosion tore through the madrassa in Peshawar, about 170 kilometres (around 100 miles) west of Islamabad, said Waqar Azim, a senior police official.

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"The blast took place in a seminary during a Koran class. Someone took a bag inside the seminary," Azim told the media.

He added that the person who had brought in the bag left the lecture hall before the blast at the Jamia Zuberia seminary.

Pakistani rescue workers and police officers examine the site of a bomb explosion in Peshawar, Pakistan. AP

Mohammad Ali Gandapur, another senior police official, said at least seven people had been killed with more than 50 wounded.

The death toll was confirmed by Mohammad Asim Khan, a spokesman at a local hospital, who told the media that seven bodies and 70 wounded people had been taken to the facility.

"Most of those killed and injured were hit by the ball bearings and some were badly burnt," he said.

All of the dead were men aged between 20 and 40, he said. Teachers and boys as young as 7 were among the wounded.

Teacher Safiullah Khan told the media more than 1,000 students are currently enrolled at the religious school, which is roughly divided into two sections, with one for students aged 18 and older and the other for children.

Pakistani police officials examine the site of a bomb explosion in Peshawar, Pakistan, on Tuesday. AP

"The blast took place in the section where students above the age of 18 were taking a class," Khan said, adding that the wall between the two sections collapsed in the blast.

A live stream of the lesson showed a religious teacher speaking in Pashto and Arabic, explaining a saying from the Prophet Mohammed, when the explosion took place.

Shortly afterwards, rescue workers and locals were seen scouring the site and collecting students' books, caps and shoes.

End to relative calm

The loud blast, which could be heard across most parts of Peshawar, wrecked the school's interior and damaged the roof of the main hall.

No group claimed immediate responsibility for the attack, which followed months of relative calm in Pakistan.

Pakistani rescue workers examine the site in an Islamic seminary in Peshawar, Pakistan, on Tuesday. AP

Peshawar was once the epicentre of militant violence in the country, with militants targeting security forces and public spaces in the city near the northwestern frontier with Afghanistan.

Violence in Pakistan has declined in recent years following a series of military operations along the border, but militant groups are still able to carry out deadly attacks.

In 2014, Pakistan's army launched a massive offensive to wipe out militant bases in the area and end the near decade-long insurgency that has cost thousands of lives.

Agence France-Presse