Police said six suspects carrying rifles and dressed in uniforms similar to those worn by the armed services entered the governor's home in Pamplona town and opened fire.
Roel Degamo, governor of Negros Oriental province, and five others were killed in the shooting, his widow said.
"Governor Degamo did not deserve that kind of death. He was serving his constituents on a Saturday," Janice Degamo, who is also the mayor of Pamplona, said in a video posted on Facebook.
President Ferdinand Marcos condemned what he described as the "assassination" of his political ally and warned the perpetrators to "surrender now it will be your best option".
"My government will not rest until we have brought the perpetrators of this dastardly and heinous crime to justice," Marcos added.
The condition of four other people who were shot in the incident was not disclosed.
The politician was distributing aid to constituents when he was shot, provincial police spokesman Kym Lopez told AFP.
Police said they were searching for 10 suspects, including the six gunmen, who fled the scene in two SUVs and a pickup truck before abandoning the vehicles in a nearby city.
Interior and Local Government Secretary Benjamin Abalos appealed for witnesses to come forward and help police "get justice" for Degamo.
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