Khyber Pakhtunkhwa Inspector General of Police Akhtar Hayat Khan told Geo News security officials were on "high alert" throughout the province.

A state of emergency has been imposed at hospitals in Swat by the provincial health department.

CTD DIG Khalid Sohail told Geo News that the blast was "not a suicide attack".

"There was no attack or firing on the police station. The explosion occurred at a place where ammunition and mortar shells were stored," he told the news channel.

He further said that the cause of the explosion — whether negligence or something else — was being investigated.

Bomb disposal squads were also conducting an investigation, he added.

Pakistan PM Shehbaz Sharif condemned the incident and tweeted: "Strongly condemn suicide attack on CTD police station in Swat. Nation is deeply grieved over martyrdom of police officials. Our police has been the first line of defence against terrorism. We will not rest until we eliminate this scourge. My condolences to bereaved families."