Taiwan's voters on Saturday will choose local government officials in an election that will provide a window on how the 2020 presidential and legislative polls will be fought.

Depending on its outcome, it could also see a shift in how the ruling Democratic Progressive Party (DPP) handles the island's foreign relations. President Tsai Ing-wen's DPP won a majority of local government executive positions in the previous local election in 2014. Two years later, she romped to victory in 2016 with 56 per cent of the over 12 million votes cast.