A 16-year-old Taiwanese K-pop singer has apologised for holding up the flag of the Republic of China (ROC) - Taiwan's formal name - and stated that she is a "Chinese", in a video clip that many believe was recorded under duress.

It infuriated many Taiwanese on a day when they were voting for their president and Parliament.

It was thought to have had an impact similar to that of the 2004 assassination attempt on former president Chen Shui-bian when he was campaigning on the eve of polls.

It was believed that sympathy for the Democratic Progressive Party's (DPP) Mr Chen, who was seeking re-election, helped tip the vote in his favour at that time.

This time, anger at Chou Tzu-yu's "forced" apology was thought to have further propelled voters into the arms of the DPP's Ms Tsai Ing-wen and legislative candidates.

The DPP advocates keeping China at arm's length, in comparison with the Kuomintang's (KMT) Beijing-friendly stance. Recognising the traction that this incident had, the presidential candidates quickly lined up behind Tzu-yu yesterday.

After casting her vote, Ms Tsai said: "Many have seen the clip and we feel a lot of heart pain (and) anger. An ROC citizen holding her national flag should not be suppressed from doing so."

In two Facebook posts, KMT candidate Eric Chu wrote: "Chou Tzu-yu, welcome home." He added: "Our hearts are with all friends who hold and support the flag."

Taiwan President Ma Ying-jeou said Tzu-yu had no need to apologise. He later said he had asked officials to "clarify the roles of the Korean and Chinese sides in this incident and demand they seriously face it". Based in South Korea, the youngest member of girl group Twice had waved an ROC flag in a recent online broadcast.

Chinese netizens denounced Tzu-yu as an advocate for Taiwan independence.

Li Xueying and Jermyn Chow