Philippine senator Christopher "Bong" Go, the preferred successor of President Rodrigo Duterte, withdrew his candidacy for presidency on Tuesday, leaving the administration without a candidate in next year's polls.

Go, Duterte's long-time aide, had recently hinted he may pull out of the presidential contest and said the president respected his decision.

His withdrawal raises questions over whom the popular Duterte will now support in the May 2022 election. The constitution limits Philippine presidents to a single six-year term, but Duterte will be standing for a senator's seat.

"I and President Duterte are ready to support whoever will truly serve and can continue and protect Duterte's legacy toward a more comfortable and safe and prosperous life for our children," Go said in a speech streamed on Facebook.

Duterte's daughter, Davao Mayor Sara Duterte-Carpio, is running for the largely ceremonial deputy post alongside the son of late Philippine dictator and namesake, Ferdinand Marcos Jr., who has emerged as an early frontrunner.

(With input from Reuters)