TAIPEI, March 13 (Reuters) - Taiwan Vice President William Lai will on Wednesday register to run as the ruling Democratic Progressive Party's (DPP) presidential candidate, the party said on Monday, his first step to run for top office at the presidential election in January.

The move was long expected, and comes after he assumed the DPP's chairmanship in January this year after President Tsai Ing-wen resigned as chairwoman in November following the DPP's trouncing at local elections.

Tsai cannot run again as president due to constitutional term limits.

The DPP said in its statement about Lai that a primary will be held if there are two or more candidates. He is by far the favourite to win the nomination.

The DPP cited Lai as saying at a party meeting that everyone needed to "unite and cooperate" and "fight together".

As in the last election in 2020, which the DPP won handily by promising to stand up to China, relations with Beijing are likely to top the agenda for 2024, especially as China ramps up pressure to get Taiwan to accept Chinese rule.

Lai angered China in 2018 while he was premier, telling parliament he was a "Taiwan independence worker" and that his position was that Taiwan was a sovereign, independent country - a red line for Beijing.

Asked about those comments in January, upon becoming party chairman, Lai said he was committed to following Tsai's policy that includes stating only Taiwan's people can decide their future, and that the Republic of China - Taiwan's formal name - and the People's Republic of China are "not subordinate to each other".

China has refused to talk to Tsai since she first took office in 2016, believing her to be a separatist. Taiwan's government strongly rejects China's sovereignty claims.

Taiwan's main opposition party, the Kuomintang or KMT which traditionally favours close ties with Beijing, has not decided on its presidential candidate yet.

Hou Yu-ih, the KMT mayor of New Taipei city, is considered by party sources a potential frontrunner as their candidate, but he has not confirmed he is running.