Vice-president of the Philippines, Sara Duterte, has held a press conference to announce that she has directed an assassin to kill President Ferdinand Marcos Jr if she herself was killed.

In a dramatic sign of a widening rift between the two most powerful political families in the south-east Asian country, Ms Duterte told the press conference before dawn that she instructed the assassin to also kill president Marcos's wife and the speaker of the Philippines House.

"I have talked to a person. I said: 'If I get killed, go kill BBM [Marcos], [first lady] Liza Araneta, and [speaker] Martin Romualdez. No joke. No joke," Ms Duterte said. 

The vice-president's comment came after an online commenter urged her to stay safe, saying she was in enemy territory at the lower chamber of Congress overnight with her chief of staff.

Ms Duterte did not say there was any alleged threat against herself.

In response to her comments, the Presidential Security Command said it had heightened and strengthened security protocols.

"We are also closely coordinating with law enforcement agencies to detect, deter and defend against any and all threats to the president and the first family," the command said in a statement.

Police chief Rommel Francisco Marbil also confirmed that an immediate investigation had been ordered into Ms Duterte's claims, and said "any direct or indirect threat to [the president's] life must be addressed with the highest level of urgency".

Under the Philippine penal code, such public remarks as those made by Ms Duterte may constitute a crime of threatening to inflict a wrong on a person or his family and is punishable by a jail term and fine.

Ms Duterte told reporters on Saturday that "thinking and talking about it is different from actually doing it". She said she is also aware of threats made against her life.

"When [my death] happens, there will be an investigation on my death. The investigation on their deaths will be next," she said.

Ms Duterte is the daughter of president Marcos' predecessor and resigned from the Marcos cabinet in June while remaining in her role as vice-president.

The move signalled a collapse of a formidable political alliance that helped the duo to secure an electoral victory in 2022 by wide margins.

Speaker of the Philippines House, Mr Romualdez, is a cousin of President Marcos and has slashed the vice-presidential office's budget by nearly two-thirds.

In October, Ms Duterte accused President Marcos of incompetence and said she had imagined cutting his head off. The two families remain at odds over issues including foreign policy and former President Rodrigo Duterte's deadly war on drugs.

Jean Encinas-Franco, a political science professor at the University of the Philippines, said that Ms Duterte's strong comments against the president will likely not impact her political support.

"If anything, this type of rhetoric brings her even closer to what her father's supporters liked about him," Ms Encinas-Franco said.

In the Philippines, the vice-president is elected separately from the president and has no official duties. Many vice-presidents have pursued social development activities, while some have been appointed to cabinet posts.

The country is gearing up for mid-term elections in May, seen as a litmus test of president Marcos' popularity and a chance for him to consolidate power and groom a successor before his single six-year term ends in 2028.

Past political violence in the Philippines has included the assassination of Benigno Aquino as he exited his plane upon arrival home from political exile in 1983.

ABC/AP/Reuters