SEOUL, South Korea — A Chinese dissident who fled the country aboard an inflatable boat has been detained in South Korea, with rights groups calling for him to be granted asylum after three previous escape attempts led to his being returned to China.

Dong Guangping, 68, a former police officer who has been imprisoned multiple times over his criticism of China’s ruling Communist Party, was detained late Monday by the South Korean coast guard, a spokesperson told NBC News on Wednesday.

Authorities detained Dong off Taean in South Chungcheong province after he was spotted by a fishing vessel, which alerted officials. Dong’s rubber boat was about 11 feet long and had a 9.9-horsepower engine, the spokesperson said.

An arrest warrant is being sought on suspicion of violating immigration laws and an investigation is underway, “while leaving open various possibilities,” the spokesperson said.

The New York Times first reported Dong’s arrival in South Korea. His lawyer, Kim Joo-kwang, could not immediately be reached for comment.

In a post on X, Chinese Canadian rights activist Sheng Xue called Dong “incredibly tenacious and brave.”

“He had previously discussed with me the idea of escaping by boat, and I thought it was far too dangerous. But he actually went through with it,” she wrote.

Sheng added that she had been in touch with Dong and that he said he had lost consciousness by the time he reached South Korean waters, having spent more than 30 hours at sea since he left Weihai, a coastal city in China’s eastern province of Shandong.

Asked about Dong at a news conference Wednesday, Chinese Foreign Affairs Ministry spokesperson Mao Ning said she was “not familiar” with the details.

According to the New York-based rights group Human Rights in China (HRIC), Dong, who is from the central Chinese city of Zhengzhou, was dismissed from the police force in 1999 after he signed a petition supporting victims of the 1989 Tiananmen Square crackdown on pro-democracy protesters in Beijing.

He was imprisoned from 2001 to 2004 after he was convicted of “inciting subversion of state power,” and he was detained again in 2014 and held in solitary confinement for more than eight months for participating in Tiananmen Square commemorations.

In 2015, Dong and his family fled to Thailand, where the United Nations High Commissioner for Refugees recognized them as refugees and they were approved for resettlement in Canada. Before Dong could leave, however, Thai authorities deported him to China, where he served another prison sentence from 2016 to 2019.

The rest of his family continued on to Canada.

Facing continued surveillance, harassment and persecution in China, HRIC said, Dong tried to swim to Taiwan’s Kinmen Islands in December 2019 but was intercepted and returned. A month later, he escaped to Vietnam, but in 2022 Vietnamese authorities deported him to China, where he was sentenced to 11 months in prison for “illegally crossing the border.” He was released in October 2023.

HRIC urged South Korea, which rarely accepts refugees aside from North Korean defectors, not to return Dong to China, saying he “faces a grave risk of persecution and torture.”

“For more than a decade, he has never ceased striving for liberty and reunion with his family,” the group said. “That a man nearing seventy years old was driven to cross open seas in a small inflatable boat is itself a devastating indictment of China’s human rights situation.”

The Chinese and Canadian embassies in Seoul did not immediately respond to requests for comment.

Dong’s detention comes at a tricky time for South Korea as it tries to improve ties with China, its biggest trading partner. South Korean President Lee Jae Myung said this year he hoped to open a “new phase” in relations with Beijing after a meeting with Chinese leader Xi Jinping.

It is not the first time a critic of the Chinese government has fled to South Korea.

In August 2023, Kwon Pyong, an ethnic Korean Chinese dissident who said he feared for his safety, fled China on a jet ski and traveled hundreds of miles by sea, trailing barrels of fuel behind him before he washed up on South Korea’s coast, where he was detained and charged with entering the country illegally.

After he was initially prohibited from leaving South Korea, Kwon told the Times in June 2024 that he was flying to Newark, New Jersey, and that he planned to apply for asylum in the U.S. or Canada.

Stella Kim reported from Seoul and Jay Ganglani from Hong Kong.