The Philippine Senate on Monday evening formally initiated proceedings against Vice-President Sara Duterte as it referred a complaint to its Committee on Rules that could lead to the convening of an impeachment court.

The move came after Senate President Francis Escudero took his oath as presiding officer of the impeachment court, in a symbolic step seen as a prelude to the trial, the Philippine News Agency reported.

Senator Joel Villanueva made the motion to refer the complaint to the Committee on Rules during the plenary session, following a manifestation from Minority Leader Aquilino "Koko" Pimentel III urging the chamber to immediately begin trial proceedings as mandated by the Constitution.

Pimentel cited Article XI, Section 3 (4) of the 1987 Constitution, which states that once a verified complaint is endorsed by at least one-third of the House of Representatives, the Senate "shall forthwith proceed" to try the case.

Escudero's oath as presiding officer, administered on the floor, came more than four months after the House of Representatives impeached Sara Duterte on charges of corruption, misuse of confidential funds, and threatening President Ferdinand R. Marcos Jr. and other officials.

The impeachment complaint was transmitted to the Senate on Feb 5.

The Committee on Rules is now tasked with determining the schedule and procedures for the trial, including the formal swearing-in of senators as judges.

Sara Duterte's allies, meanwhile, are drafting a resolution seeking dismissal of the case on grounds of inaction.

If convicted by two-thirds of the Senate, she would be removed from office and permanently barred from holding public office.

This is the fifth impeachment case in Philippine history and the first involving a vice president.