Three journalists have been gunned down in the Philippines in its worst spate of media killings in nearly four years, police and rights watchdogs said Friday.

The latest victim, freelance news photographer Mario Sy, was killed in front of his wife and child late Thursday by two suspects who broke into his home in the southern city of General Santos, police said.

Sy's 15-year-old daughter Marisol said her family had just finished dinner when the gunmen struck.

"One unidentified man barged in and shot at him. My father was not hit but the gunman got closer and shot him again," she told reporters.

"I ran outside and saw the suspect walking casually toward his companion, who was waiting outside. They disappeared in the dark," she said.

The attack followed the shooting deaths in Manila on Tuesday of two columnists on a tabloid newspaper that had recently ceased publication, said Rupert Mangilit, secretary-general of the National Union of Journalists of the Philippines.

"We're quite alarmed that despite claims that the environment for journalists is safer now, we have three killings happening in a week," he told AFP.

The New York-based Committee to Protect Journalists says at least 73 Philippine journalists have been killed in direct connection to their work since 1992, making it the second deadliest country in the world for the press.

Critics blame this on widespread gun ownership by civilians and a "culture of impunity" that sees many among the powerful not being brought to justice for criminal acts.

Thirty-two journalists were among 58 people kidnapped and murdered allegedly by a powerful political clan in the southern province of Maguindanao in November 2009.

"Since the Maguindanao massacre this marked the first time that we had more than two journalists killed in a week," Mangilit said.

General Santos police investigator Fernando Torreta said the authorities have yet to establish the motive for the attack on Sy, 53.

However Sy's publisher, John Paul Jubelag of local paper Sapol News said that he had been openly critical of neighbourhood drug dealers.

"Mario was very vocal against the alleged open illegal drugs trade in their area. I think, the police should start their investigation by looking at this angle," he said.

Mangilit said the two slain Manila columnists, Richard Kho, 47 and Bonifacio Loreto, 59, had both worked for a small tabloid called Aksyon Ngayon (Action Today) that folded in March.

Both had tackled "political" issues that could have won them enemies, he added.

Carlos Conde, a Philippines researcher for the international rights watchdog Human Rights Watch, told AFP: "It is indeed very worrisome... For human rights in general and extra-judicial killings and summary killings in particular, it seems things are not improving."

He said reports of summary execution-style killings in general are on the rise in Manila as well as provincial centres.

Only three people have been convicted of murdering journalists in the Philippines since President Benigno Aquino came to power in 2010, Conde said.

In the same period, Mangilit said, 18 other journalists were murdered across the country.