China has displaced longtime foe and former colonial power Japan in many South Koreans' minds as the country's most distrusted neighbour in recent years.

And ahead of Tuesday's vote, anti-Chinese feeling has spread among South Koreans -- online, at right-wing rallies and in Seoul's Chinatown.

Many of the quarter's Chinese residents, such as 74-year-old Yu Shunzi, flocked to South Korea seeking economic opportunities in the 1990s and 2000s.

"A lot of Koreans still think China is a very backward country and discriminate against Chinese a lot," she told AFP.

Yu, who arrived in 2007 from the northeastern Chinese province of Heilongjiang, said the situation is so bad that she planned to move back when the economy allowed.

"I want to go home, but with the exchange rate being this low, I'd lose a lot of money," she said.

While former colonial master Japan has long had a difficult relationship with South Korea, Seoul's ties with China have increasingly come under the spotlight.

In 2022, polling conducted by Hankook Research showed for the first time that South Koreans distrusted China more than they did Japan -- a trend that has continued in recent years.

- 'No affinity' towards China -

Former leader Yoon Suk Yeol referred to vague allegations of Chinese spying when he tried to justify his declaration of martial law, which led to his ousting.

Conspiracy theories have since run rampant among the South Korean right, fuelling the distrust.

But analysts also say that a series of clashes between Beijing and Seoul in recent years over history, territory and defence are the deeper cause of the schism.

"China's growing assertiveness is the main reason behind South Korea's negative views about the country," said Ramon Pacheco Pardo from King's College London.

"Most South Koreans have no affinity towards today's China," the international relations professor told AFP.

Seoul has long trodden a fine line between top trading partner China and defence guarantor the United States.

Relations with China nosedived in 2016 following the South's decision to deploy the US-made THAAD missile defence system.

Beijing saw it as a threat to its own security and reacted furiously, imposing a string of restrictions on South Korean businesses and banning group tours as part of sweeping economic retaliation.

A series of public spats about the origins of Korean cultural staples such as kimchi, which China had claimed as its own, also left a bitter taste.

Yoon's administration deepened that divide, cleaving close to the United States and seeking to improve ties with Japan.

"Under his leadership, Seoul made its position unmistakably clear: it stood with Washington and its allies, not Beijing," Claudia Kim, assistant professor at City University of Hong Kong, told AFP.

Opposition leader and election frontrunner Lee Jae-myung has publicly hinted that a softer line might be in the works if he wins.

Beijing won't "miss the opportunity to improve relations with the South" if Lee wins, Cheong Seong-chang at Seoul's Sejong Institute told AFP, suggesting a visit by Chinese President Xi Jinping could even take place.

Lee has also raised alarm bells by saying that a future conflict between China and Taiwan would not be South Korea's concern.

That could put him on a collision course with the administration of US President Donald Trump, which has made containing China a cornerstone of its bid to reshape the international order.

"Trump's focus on deterring China may lead to a mismatch of foreign policy priorities with Lee," Edward Howell, a lecturer in politics at the University of Oxford, told AFP.

- Fake news thrives -

Compounding deepening distrust of China has been a surge of conspiracy theories.

Analysis by AFP revealed many of the most widely-circulated pieces of misinformation tap into fears of meddling by China.

Rallies in support of ex-president Yoon have featured calls to oust alleged "pro-Chinese Communist Party" forces, as well as posters with anti-Chinese slurs and slogans advocating for Chinese nationals to be deported.

A recent editorial in Beijing's state-run nationalist tabloid Global Times condemned "far-right" forces in South Korea for "stirring up xenophobia" against Chinese people.

In Seoul's Chinatown, Li Jinzi, 73, complained about a culture of "misinformation" that was breeding negative feelings towards her home country.

"Fake news breeds misunderstandings," she said.