At least 30 people are feared dead and around 300 injured after a suicide bomber blew himself up in Lahore, Pakistani police have said.

Rescuers try to free a trapped policeman while an armed colleague keeps a lookout

The powerful blast outside the office of the emergency police service caused widespread destruction, bringing down a government ambulance service building.

The nearby office of Pakistan‘s main intelligence agency was also badly damaged.

Local government official Khoro Pervaiz told Dawn news channel that “there is a large number of casualties”.

The administrator of the main hospital, Ganga Ram Hospital, says 300 hospital beds have been prepared and 12 people have died at his hospital.

Some 112 people have been admitted suffering injuries, said Dr Fayez Ranjha.

A government official put the death toll from the blast at 30.

Sporadic gunfire was heard in the area of the blast as troops rushed to the scene and commandos took up position on the rooftops of damaged buildings.

Local TV footage shows two alleged suspects being arrested

Two suspects have been arrested – television footage shows one being escorted away by police as the crowds try to attack him.

Sky’s Asia correspondent Alex Crawford there are still reports of four “attackers” holed up inside the Central City Police Office (CCPO) and ongoing firing.

Sky News has spoken to the telephone operator who is still trapped inside the police station, which he says is partly destroyed.

He is unable to say whether anyone else is inside but police are going through the CCPO room by room, searching for attackers, Crawford added.

An eyewitness said he saw a white Toyota Hiace draw up near the police station and people were firing out of it, she went on.

“He then saw three to four people get out – we don’t know what happened to them.”

Shortly after the explosion, emergency workers were seen carrying at least one body covered by a blanket to an ambulance and people are still being pulled from the rubble.

“It was a strong bomb blast. It damaged several buildings and cars and shattered windows,” said police spokesman Nayyab Haider.

There has been no claim of responsibility but it comes as the army is battling militants in the Swat region in the northwest of the country in its most concerted action to push back a growing Taliban insurgency.

“I believe that anti-Pakistan elements, who want to destabilise our country and see defeat in Swat, have now turned to our cities,” Interior Ministry chief Rehman Malik said.