China said "reunification" with Taiwan remained "inevitable" after president-elect Lai Ching-te won Saturday's pivotal election on the self-ruled island that Beijing claims as its own.

Lai, branded by China as a threat to peace, won an unprecedented third consecutive term for Taiwan's ruling Democratic Progressive Party (DPP) after he pitched himself as the defender of the island's democratic way of life.

In a statement issued after Lai emerged as the winner, Beijing's Taiwan Affairs Office spokesperson Chen Binhua said in a statement that the vote "will not impede the inevitable trend of China's reunification", according to state news agency Xinhua.

The results of the vote, Chen said, showed that the DPP "cannot represent the mainstream public opinion on the island".

Chen also said the vote "will not change the basic landscape and development trend of cross-Strait relations".

Beijing's stance on "realising national reunification remains consistent, and our determination is as firm as rock", he said, adding that "Taiwan is China's Taiwan". 

He said Beijing "firmly oppose(s) the separatist activities aimed at 'Taiwan independence' as well as foreign interference".

The election was watched closely by both Beijing and Washington, Taiwan's main military partner, as the two powers tussle for influence in the strategically vital region.

In a New Year's address, Chinese President Xi Jinping had said the "unification" of Taiwan with China was "inevitable".

And in the run-up to the vote, Beijing warned that Lai was a "severe danger" who would threaten peace by following the "evil path" of independence.