ISLAMABAD, Nov. 21 (Xinhua) -- At least three children were killed and two others critically injured in a blast on Wednesday in Pakistan's northwest Swat district, local media reported.

According to local Urdu channel Geo TV, the blast took place when the children were playing with a mortar shell in a field in Arkot village of Mata area in Swat, a district in northwest Khyber Pakhtunkhwa province.

Police and rescue teams rushed to the site and shifted the bodies and injured to the nearby hospital.

Local police said that the explosion was triggered when the children started throwing the live mortar shell to each other considering it as a toy.

Police said the mortar was fired from an unknown location, which missed its target and did not explode also.

Police have registered a case and launched a search operation to make sure that no other shell is present in the area.