A gunman opened fire outside a terminal at Manila's main airport on Friday, killing Mayor Ukol Talumpa, his wife, another male family member and a child.
The gunman approached Talumpa, mayor of southern Philippines town Labangan, and shot him and the other three at close range.
The shooter then escaped. The motive behind the shooting is unclear.
"The mayor and his family and some security escorts were attacked," said airport manager José Angel Honrado.
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"Government agencies are trying their best to determine the perpetrators and bring them to justice," he said.
The Ninoy Aquino airport is home to both international and domestic flights, and was crowded with holiday travelers at the time of the shooting.
Initial reports said there was more than one shooter involved in the incident, but police said they believe it was a single gunman who fired at the mayor, his family and his security detail before taking off on foot and being picked up by an accomplice on a motorcycle.
At least five others were injured during the shooting, including the mayor's three-year-old niece, who sustained a head wound.
Police said the mayor, who had survived previous assassination attempts, was the target of the shooting.
In 2010, when Talumpa was vice mayor, he and one of his nephews were wounded in another attack in Manila. Last year, assailants threw a grenade at Talumpa and his wife in Pagadian City, but they escaped unharmed.