KAOHSIUNG, Taiwan - Tens of thousands of people gathered in southern Taiwan for "Super Sunday" rallies by three presidential candidates making a final weekend push before a crucial January 13 election.

The poll is being closely watched from Beijing to Washington, with the winner set to determine the future of the democratic island's relations with an increasingly aggressive China.

Beijing claims Taiwan as part of its territory, and President Xi Jinping has in recent years intensified rhetoric about "unification" while refusing to rule out the use of force to bring it under Chinese control.

Frontrunner and current Vice President Lai Ching-te of the ruling Democratic Progressive Party (DPP) has called the election a choice "between democracy and autocracy", while his main opponent Hou Yu-ih has warned the DPP will bring Taiwan "closer to war".

Speaking to a sea of green-clad supporters -- DPP's colours -- in Kaohsiung, where all three candidates sought to rally the agricultural south, Lai called for voters to stand "side-by-side with the democratic camp".

"Facing the threat from China, we must work together and be united," he said.

"Lai Ching-te and (running mate) Hsiao Bi-khim are ready."

The two have been blasted as an "independence duo" by Beijing, which loathes the DPP and current President Tsai Ing-wen for defending Taiwan as a sovereign state separate from China.

China has cut off high-level communications with Tsai during her eight-year tenure and dispatched unprecedented numbers of fighter jets and naval vessels around Taiwan -- a ramp-up in military pressure that has raised global fears of a potential conflict.

Lai, Tsai's deputy, has in the past been far more vocal about independence -- a red line for Beijing -- but has softened on the issue in recent months.

Appearing on stage with him Sunday, Tsai said their eight years "of hard work cannot be wasted".

"I would like to call on everyone not to turn around or look back on the road to democracy," she said.

"Not only does the world recognise Taiwan now, they also invest in Taiwan, which means that Taiwan is safe. The consensus among democratic countries in the world is also to jointly safeguard peace and stability across the Taiwan Strait."

Some of the estimated 120,000 supporters in attendance voiced the same worries about China's encroachment.

If Taiwan elects the wrong person, cross-strait relations will "be a danger", said Yang, a resident care attendant.

"We can't return to the... 'one family across the strait' concept," the 42-year-old told AFP, referring to a common refrain espoused by Beijing's leadership about Taiwan.

"Taiwan is a free and democratic country, we don't like living a life with our hands and feet tied."

- Fears of war -

In a neighbouring district, Hou -- the candidate for Kuomintang (KMT), which endorses closer relations with Beijing -- called on voters not to be "deceived" by the DPP.

"They love to say Hou Yu-ih is pro-China and will sell out Taiwan," the 66-year-old New Taipei City mayor shouted. "Hou Yu-ih will look after cross-strait peace."

A former policeman who has portrayed himself as a "protector" of Taiwan, he said Taiwan "must not let such a party (DPP) continue to be in power."

KMT supporter Ou Pei-li said she was worried about a war breaking out with China.

"I don't want it to be like the Ukraine-Russia war," said the 56-year-old, who works in finance, surrounded by people carrying signs that said "Vote KMT, Taiwan Strait will be free of wars".

Meanwhile, third-party candidate Ko Wen-je held a competing rally near Kaohsiung's city centre.

The head of the small Taiwan People's Party (TPP), Ko has made an unexpected splash, drawing young voters with his brash rhetoric and criticism of the DPP and KMT.

This election is "a face-off between new politics and old forces", Ko declared in a speech.

The mostly younger crowd at TPP's rally agreed, many of them donning a headpiece shaped as a blade of grass to represent Ko's grassroots support.

"The KMT is too pro-China... and the DPP doesn't engage in dialogue at all," said 34-year-old Tang Shu-feng.

"I think Taiwan needs a change, so I want to try someone different."