A radio broadcaster known for hard-hitting commentaries against local officials has been shot dead in the Philippines while on his way to work, authorities say.

Joey Llana, 38, a broadcaster with DWZR, was driving his vehicle to work when unidentified gunmen ambushed him along a highway in Daraga town in Albay province, 336 kilometres south of Manila.

Llana suffered multiple gunshot wounds to the head and body, said Senior Inspector Maria Luisa Calubaquib, a regional police spokeswoman.

Calubaquib said investigators were still determining a motive for the killing, but noted that Llana had reportedly received death threats due to comments made on his radio programs.

"If proven to be related to his work, his death would be the 12th media killing under President Rodrigo Duterte . and the 185th since 1986," according to the National Union of Journalists of the Philippines.

The Philippines has been ranked as one of the world's most dangerous places for journalists by press freedom groups, including the New York-based Committee to Protect Journalists.

In 2009, 32 media workers were among more than 50 people killed in a local politician's convoy heading to a rally in the southern region of Mindanao. The alleged masterminds are currently on trial.