As many as 10 children were drowned and 10 others were fished out when a boat carrying more than 25 kids capsized in Tanda Dam of Kohat on Sunday, reported 24NewsHD TV channel.
In the rescue operation which started soon after the tragedy, the divers took out 10 students alive while they also retrieved 10 dead bodies of the kids.
They were shifted to the hospital.
According to the hospital sources, the condition of the rescued children was critical.
The rescue teams were still searching for other children.
The children are students of a religious seminary, Madrassa Arabia Mir Bash Khel.
A special diving team has also been dispatched from Peshawar for the rescue operation.
In Khyber Pakhtunkhwa, local police official Mir Rauf told AFP all of the dead so far recovered from the lake were between the ages of seven and 14.
He said 11 more children had been rescued, with six in critical condition. However, up to nine more remain missing from the madrassa class which was day tripping at the scenic location.
"A rescue operation is underway," Rauf told AFP.
Reporter Kamran Bangash and input from AFP