Authorities said the home-made explosive device exploded in the town of Parang, Maguindanao province and was apparently planted by political rivals of the local town mayor, Vivencio Bataga, who survived the attack.
"The mayor was wounded but he is fine. I saw 10 people dead," said town councillor Gaudencio Teves, adding that 40 others were rushed to different hospitals.
Many of those injured by shrapnel and the stampede that followed were children and women, police said, while a man believed to have planted the bomb was among the fatalities.
Regional police chief Isnadji Bantala said no-one had claimed responsibility for the bombing, but ruled out involvement of Muslim separatists and the Al-Qaeda linked Jemaah Islamiyah (JI) group.