This is a developing story. Photograph: (WION)
Several students are feared to have been held hostage, though the gunmen attacked before class was scheduled to start
A gun battle with security forces is taking place between suspected members of the Bangsamoro Islamic Freedom Fighters (BIFF) group and security forces, according to Chief Inspector Realan Mamon.
Reuters reports that several students are being held hostage, but the mayor was unable to confirm that earlier, and stated that the gunmen attacked the school before class was scheduled to start.
The IS-linked militants are being led by one "Commander Agila", in the village of Barangay Malagakit, reports the Philippines daily, Inquirer.
The mayor is still seeking information about possible casualties. He confirmed that civilians were trapped.
President Duterte declared a state of emergency on Mindanao island last month, as Islamic State-linked fighters were embroiled in a siege on Marawi City, now in its fifth week.
They are on the same island, but there is as much as 190 kilometres separating Pigcawayan from Marawi city. An Al Jazeera reporter speculated that the state of martial law across the region may be a type of link.
This story will be updated as new reports come in.