By Agence France-Presse
The island-wide vote for political representatives, from village up to city level, is a mid-term test for embattled President Tsai Ing-wen as she faces a backlash over domestic reforms and concerns about deteriorating ties with China.
The ballot also features 10 referendums, including pro- and anti-gay marriage votes and a bid to change the name under which Taiwan competes at international sports events that has already angered China.
There were long queues at polling stations Saturday morning with Tsai urging people to come out and vote as she cast her ballot in New Taipei City.
"I feel that this is a democratic society and people can express their views on many issues," she told reporters.
College student Kwan Chin-shun, 18, voting in Taipei, said she wanted to support the referendum calling for equal marriage rights.
"There's nothing wrong with loving someone of the same sex," he told AFP.
There are competing referendums on gay rights, with "pro-family" groups calling for marriage to be legally defined as between a man and a woman.
A landmark court decision legalising gay marriage is still to be implemented and LGBT groups are concerned a referendum win for conservative campaigners could limit their newly won rights.
- 'Outside forces' -
The referendums come as an extra headache for Tsai and her ruling Democratic Progressive Party (DPP), which faces strong challenges in major seats.
Tsai has framed the local elections as a way to "tell the world" that Taiwan will not bow to Beijing, which has ramped up military and diplomatic pressure since she took office in 2016.
China sees self-ruling Taiwan as part of its territory and is incensed that Tsai will not acknowledge the island as part of "one China", unlike her predecessor Ma Ying-jeou of the Beijing-friendly Kuomintang party (KMT).
Tsai was voted president by a landslide two years ago as the public feared the KMT were getting too close to Beijing, and she has played up the importance of Taiwanese identity on the campaign trail.
She has called China's pressure "omnipresent", flagging up a recent row at the Golden Horse film awards in Taipei which saw a mainland actor referring to the island as "China, Taiwan" after a Taiwanese filmmaker had voiced her support for independence.
Taiwan's Investigation Bureau also says it is probing Chinese influence on the elections through campaign funding of candidates.
At a final campaign rally Friday night in Taipei, Tsai said Taiwan's democracy was faced with a crisis due to "outside forces".
But the KMT is billing the local polls as a vote of no confidence in Tsai, vowing to promote peaceful relations with China and boost the economy.
Tsai's pension and labour reforms have been unpopular and despite a growing GDP, some voters complain they have not seen any benefits as salaries remain stagnant and the cost of living rises.
Some also blame cross-strait tensions for denting their livelihoods, including grass-roots groups that traditionally vote DPP.
Tsai Bao-hsing, head of Liuchiu Fisherman Association in Pingtung county, Tsai's home town, told AFP many of the group's members would vote KMT to "punish the DPP" for failing to promote the export of fish products to China as Taiwan seeks to diversify to other markets.
Polls close at 4:00 pm local time (0800 GMT) with results not expected until late Saturday.