Taiwanese voters are deciding whether to remove about one-fifth of their lawmakers from the opposition Nationalist Party.

Voters in Taiwan were casting ballots on Saturday on whether to recall one-fifth of the island's parliament, all from the major opposition party, in a move supporters hope will send a message to China and opponents say is an assault on democracy.

Thousands of Taiwanese are heading to the polls in an unprecedented and controversial vote aimed at ousting lawmakers accused of being too close to China. More than 30 lawmakers have been targeted in the "dabamian", or Great Recall vote, initiated by a civic movement.