Taiwan President Tsai Ing-wen has named as her running mate for 2020 elections a former prime minister who last year angered Beijing so badly with his support for the island's formal independence that a major Chinese paper called for his arrest.

Self-ruled and democratic Taiwan is claimed by China as a wayward province and is the Communist Party's most sensitive and important territorial issue. China has threatened to attack if Taiwan moves towards independence.

William Lai, prime minister until January, when he stepped down to take responsibility for a crushing defeat in regional elections last November for the ruling Democratic Progressive Party, will be Tsai's vice president candidate, she told a news conference in Taipei on Sunday.