Broadcaster Rudy Alicaway and columnist Leo Diaz were the third and fourth journalists to be killed since President Rodrigo Duterte, a vocal critic of the press, took office last year, said Dabet Panelo, secretary-general of the National Union of Journalists of the Philippines (NUJP).
In both cases the victims were riding motorcycles when gunmen on another motorcycle came up behind and shot them dead.
Diaz, 60, a correspondent of Manila tabloid Balita (News) and a columnist for a community newspaper, was killed in the southern town of President Quirino on Monday, said Fort Yerro, a Balita consultant.
Alicaway, 47, who hosted a weekly community affairs show on DXPB radio station, was killed in the town of Molave on Sunday, a police report said.
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"We are asking ourselves why this happened to him. He had no enemies as a broadcaster," Navarro told AFP.
Both killings took place on the southern island of Mindanao, where Islamic militants, communist guerrillas and political warlords are active.
Last week Michael Marasigan, a respected former newspaper editor, was shot dead in a Manila suburb.
A study by the International Federation of Journalists said last year that 146 journalists were killed between 1990 and 2015, making the Philippines the second most dangerous country for the media after Iraq.
Duterte, who took office last year, has lashed out at journalists over critical coverage of his anti-drug war that has claimed thousands of lives.
"Just because you're a journalist you are not exempted from assassination, if you're a son of a bitch," he said.