Taiwan's frontrunner presidential candidate Lai Ching-te took a clear lead in the vote count Saturday, according to partial results, after China warned electing him would lead to "war and decline" for the self-ruled island.
Beijing has in the past slammed Lai, the current vice president, as a dangerous "separatist" and on the eve of the vote, its defence ministry vowed to "crush" any move towards Taiwanese independence.
Communist China claims democratic Taiwan, separated from the mainland by a 180-kilometre (110-mile) strait, as its own and says it will not rule out using force to bring about "unification", even if conflict does not appear imminent.
With ballots counted from more than 60 percent of polling stations, Lai of the Democratic Progressive Party (DPP) was on 41.6 percent of the vote, according to official data from Taiwan's Central Election Commission.
His nearest rival Hou Yu-ih of the opposition Kuomintang (KMT) trailed in second place with 33.2 percent.
Nearly 20 million people were eligible to vote, and turnout has not yet been announced.
Full results are expected before the night ends, with the outcome watched closely by both Beijing and Washington, Taiwan's main military partner, as the two superpowers tussle for influence in the strategically vital region.
Lai, 64, pitched himself during a raucous campaign as the defender of Taiwan's democratic way of life.
"This is Taiwan's hard-won democracy. We should all cherish our democracy and vote enthusiastically," Lai told reporters as he voted in a school gymnasium in the southern city of Tainan.
KMT's Hou, 66, favours warmer ties with China and accuses the DPP of antagonising Beijing with its stance that Taiwan is "already independent".
The KMT has said it will boost economic prosperity while maintaining strong relationships with international partners, including the United States.
"I hope that no matter how turbulent it was during the election process, everyone will unite after the poll to face Taiwan's future," Hou told reporters after voting in New Taipei City.
The race has also seen the rise of the upstart populist Taiwan People's Party (TPP), whose leader Ko Wen-je has drawn support with an anti-establishment offer of a "third way" out of the two-party deadlock.
In the three parties' campaign headquarters, supporters waited as poll stations across the island counted the votes by hand.
University student Su, a DPP supporter, said he hopes that Taiwan can one day be recognised by the world as a country.
"If war would happen no matter who we choose, choosing DPP can at least make it clear to the world that we are not choosing China," he said, while keeping a close eye on changing numbers of the count.
- China censorship -
Located on a key maritime gateway linking the South China Sea to the Pacific Ocean, Taiwan is home to a powerhouse semiconductor industry producing precious microchips -- the lifeblood of the global economy powering everything from smartphones and cars to missiles.
China has stepped up military pressure on Taiwan in recent years, periodically stoking worries about a potential invasion.
Chinese President Xi Jinping said in a recent New Year's address the "unification" of Taiwan with China was "inevitable".
As voters cast their ballots across the strait, AFP reporters spotted a fighter jet in the skies above the island of Pingtan, the nearest point in China to Taiwan's main island.
The hashtag "Taiwan election" was a top trending item on China's social media platform Weibo before being blocked at around 9:45 am (0145 GMT).
Chinese warplanes and naval ships probe Taiwan's defences almost daily and Beijing has also staged massive war games in recent years -- simulating a blockade of the island and sending missiles into its surrounding waters.
The Chinese military said the night before the polls that it would "take all necessary measures to firmly crush 'Taiwan independence' attempts of all forms".
US Secretary of State Antony Blinken met a senior Chinese official in Washington hours before the vote and stressed the importance of "maintaining peace and stability" across the Taiwan Strait.
Under Taiwanese law, President Tsai Ing-wen could not run again because she has served the maximum two four-year terms.
As well as a president, voters are also electing lawmakers to Taiwan's 113-seat legislature.