Polling stations opened at 8 a.m. and will close at 4 p.m., reports Efe news
More than 19 million voters, including nearly one million new ones, are eligible to cast their ballots for their next President, as well as 113 parliamentar, in an election considered crucial in deciding the future of the relationship of the island with China and the US.
Tsai, leader of the Democratic Progressive Party (DPP), was among the first voters in the polling station in her constituency in the capital, Taipei, and urged the people to come out and vote in large numbers to strengthen democracy in Taiwan.
Han, too, went early to vote in the southern city of Kaohsiung, the country's second-largest metropolis - of which he is the current mayor - while being accompanied by his daughter, Han Bing.
According to the latest polls, published 10 days ago, Tsai enjoyed a clear 20-point lead, overturning a situation of relative disadvantage six months ago.
Ongoing protests in Hong Kong, which began in June, and statements by Chinese President Xi Jinping in which he did not rule out the use of force in China's relationship with Taiwan have helped increase Tsai's support base in recent months.
The President, who advocates maintaining the current 'status quo' in the relationship with mainland China, holds a much tougher line with Beijing than Han, who is in favor of greater rapprochement with the communist regime.
"The young people of Hong Kong have used their lives, as well as their blood and tears, to demonstrate to us that 'One Country, Two Systems' is unworkable," Tsai said late Friday during an address marking the end of her election campaign in Taipei.
Although the DPP candidate appears set to cruise to victory in the presidential contest, her party may have a harder time earning a majority in parliament, according to observers.
Beijing considers Taiwan a rebel province that will need to return to its fold.
The Chinese government has suspended formal relations with Taipei since Tsai was first elected in 2016 and she refused to accept the One China policy advocated by the regime.
In the 2016 elections, Tsai won 56.12 per cent of the vote compared to 31.04 per cent by the then-Kuomintang candidate, Eric Chu.
Turnout in those elections was 66.27 per cent, the lowest among the six presidential elections held since 1996.
The DPP obtained an absolute majority for the first time, with 68 seats, while the Kuomintang won 35 seats.
( With inputs from IANS )