Taiwan's presidential rivals will hold mass rallies on Friday in a final push to convince voters ahead of a closely watched election that looks set to infuriate China and send ripples far beyond its borders.

Some 19 million people are eligible to vote on Saturday to choose between two leaders with very different visions for Taiwan's future -- in particular how close the self-ruled island should tack to its giant neighbour.

Beijing views Taiwan as part of its territory and has vowed to one day retake the island, by force if necessary.

But China is also Taiwan's largest trade partner.

President Tsai Ing-wen, who is seeking a second term, has pitched herself as a defender of Taiwan's liberal values against the increasingly authoritarian shadow cast by Beijing under President Xi Jinping.

Taiwan's relationship with China has dominated the campaign
Taiwan's relationship with China has dominated the campaign AFP / Sam Yeh

"Choosing Tsai Ing-wen... means we choose our future and choose to stand with democracy and stand with freedom," Tsai, 63, told reporters on Friday during a campaign stop.

Her main competitor Han Kuo-yu, 62, favours much warmer ties with China -- saying it would boost the island's fortunes -- and accuses the current administration of needlessly antagonising Beijing.

"We want change, we want to rediscover happiness, prosperty and pride for Taiwanese people," Han told a huge rally in the capital on Thursday night, the crowd in front a sea of swaying red and blue national flags.

Both candidates are planning final mass rallies on Friday night as they try to mop up swing voters for both the presidency and the unicameral parliament.

Taiwan bans the publishing polls within 10 days of elections but Tsai has led comfortably throughout the campaign. Her party currently has a parliamentary majority, which analysts expect them to retain.

Taiwan's President Tsai Ing-wen waves to supporters as she campaigns in Taoyuan
Taiwan's President Tsai Ing-wen waves to supporters as she campaigns in Taoyuan AFP / Sam Yeh

"It would take a huge shift from the final polls for Han to win," said Shelley Rigger, a Taiwan expert at North Carolina's Davidson College.

Beijing has made no secret of its desire to see Tsai ousted.

Her Democratic Progressive Party leans towards independence, and Tsai rejects Beijing's view that Taiwan is part of "one China".

Han Kuo-yu was a surprise choice for the KMT, but faces an uphill battle to win the presidency
Han Kuo-yu was a surprise choice for the KMT, but faces an uphill battle to win the presidency AFP / Sam Yeh

In the four years since Tsai won a landslide victory, Beijing has tightened the screw, severing official communications with her administration while ramping up economic and military pressure.

It also poached seven of Taiwan's few remaining diplomatic allies, hopeful that a stick approach would convince voters to punish Tsai at the ballot box.

But the campaign appears to have backfired, especially in the last year after Xi gave a particularly bellicose speech stating Taiwan's absorption into the mainland was "inevitable".

Taiwanese voters were increasingly rattled by China's hardline response to pro-democracy protests in neighbouring Hong Kong and the mass internment of Uighur Muslims in Xinjiang.

A year ago Tsai looked a lame-duck president, languishing in the polls after the DPP received a thumping at local mid-term elections.

But analysts say Tsai's ability to seize on the protests in Hong Kong, as well as Taiwan's successful economic navigation of the US-China trade war, have boosted her fortunes.

"Tsai has convincingly presented herself as the best person to defend Taiwan's sovereignty," Bonnie Glaser, an expert at the Centre for Strategic and International Studies, told AFP.

Her rival Han, from the opposition Kuomintang (KMT), has struggled on the campaign trail.

A plain-speaking populist, he stormed onto the political scene in 2018 when he won the mayoralty of the usually staunch DPP city Kaohsiung.

But his political momentum slowed once he became the opposition candidate as he fought to shake off accusations he lacked experience and was too cosy with Beijing.

"Han Kuo-yu was a bad choice for the KMT," said Glaser. "He has made many gaffes and provided little details about his policies."

Still, the KMT are not going down without a fight -- portraying Tsai as a dangerous leader pushing Taiwan towards conflict.

The results of Saturday's vote will also be closely watched by regional powers and in Washington, especially given the parlous state of US-China relations.

Taiwan has long been a potential flashpoint between Beijing and Washington, which remains the island's main military ally.