Philippine President Gloria Macapagal-Arroyo on Wednesday declared a national day of mourning for the victims of Monday's massacre in the country's southern province of Maguindanao.

Executive Secretary Eduardo Ermita said in a press briefing that Ms Arroyo declared the national day of mourning three days after the worst massacre in the country's history in which at least 49 people, including journalists, were brutally killed.

He said Ms Arroyo extended the government's sympathies and condolences to the families of the massacre victims by declaring a national day of mourning.

Arroyo placed three provinces in southern Mindanao region under the state of emergency on Tuesday. The Presidential Office said the move is to "prevent and suppress lawless violence" in provinces of Maguindanao, Sultan Kudarat, and Cotabato city. The order started to be in effect on Tuesday and remains so until being lifted by the president.