The shootout happened late Sunday in Quezon province, The Philippine Star reported. Thirteen people, including three members of the Philippine National Police, were killed.
A source, who spoke on the condition of anonymity due to the sensitivity of the case, told the newspaper the clash was between two rival groups of "bookies" that involved police and army personnel.
"The two groups have long been threatening each other. This has been happening since the brother of Marantan got into the bookies in Laguna," the source said.
"There are policemen and army soldiers involved; that's why they were covering it up."
Chief Superintendent James Melad said 14 firearms were recovered from the scene, four of which were unlicensed.
"What we are trying to find out is why did they have so many firearms. Why are those police officers with the group and why were they using service-issued firearms? Are these firearms licensed? Did they have the permits to carry [these guns]," Melad said.
The investigation of the incident was ongoing.