Eight others were injured, with four in critical condition, and all the victims were students aged 14 to 17, said Albert Palencia, mayor of Banga town in South Cotabato, where the shooting took place.
The incident on Friday follows two fatal gun incidents since June at schools in the Philippines, where school shootings were previously rare.
"The suspect supposedly sat beside his friends and told them to go home 'because after lunch, I will be executing my plan'. His friends laughed because the shooter was a known joker," Palencia told Reuters.
"After lunch, he started shooting students. He hit 10 students before killing himself," Palencia said.
In August, a student live-streamed himself shooting and killing another student in a classroom in Zamboanga in the country's south before taking his own life.
In June, at least three students were killed and about 20 others injured in an attack at a public high school in Tacloban, where two classmates opened fire on campus.
The Philippines has relatively strict gun ownership regulations, including background checks and psychological evaluation requirements, although illegal firearms remain in circulation.
The Friday shooting also follows a high-profile incident in Thailand in August, where a student went on a shooting rampage at a school on the outskirts of the capital Bangkok.
South Cotabato governor Reynaldo Tamayo urged parents to ensure guns were kept out of reach of minors.
"We need to be responsible in storing firearms. Gun owners, in particular, must make sure that minors do not have access to them," Tamayo told Reuters by phone.
"We cannot expect a handful of security personnel to monitor thousands of students. We need to work together because otherwise this will be very difficult for us to address."
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