Official results from the Philippines Election Commission shows key allies of detained former President Rodrigo Duterte and two liberal opposition candidates are among top winners in the nation's midterm Senate race.

Former Philippine President Rodrigo Duterte is set to return to his longtime political stronghold as Davao City mayor, winning by a landslide despite being detained at the International Criminal Court (ICC) in The Hague.

It is up to the Department of the Interior and Local Government to say who will exercise the functions of mayor of Davao City while former President Rodrigo Duterte is detained in The Hague, the Commission on Elections said on Tuesday.