He had traveled about 300km (186 miles) across the Yellow Sea using binoculars and a compass, but then got stuck.

According to local reports, he is Kwon Pyong, a critic of President Xi Jinping.

Seoul’s Chinese embassy declined to comment.

To prevent activists from leaving Chinese territory, Beijing has increased its use of exit bans at airports and other legal border crossings.

Several pro-Beijing countries in south-east Asia will no longer accept asylum seekers, making it harder for dissidents to flee.

Lu Siwei, a noted Chinese human rights lawyer, was captured in Laos last month and returned to China before joining his family.

It is perhaps one of the more extreme escape attempts seen in modern times to jet ski across choppy waters to South Korea.

He was towing five barrels of fuel from Shandong province behind the 1800cc machine, according to the coast guard.

“He refilled the petrol on the ride and dumped the empty barrels into the sea,” it said, adding he got into trouble near a cruise terminal off the western port of Incheon.

Despite not identifying the man, the coast guard said he was detained last Wednesday for trying to “smuggle himself” into the city. He is not suspected of being a spy. On Tuesday, Lee Dae-seon, a campaigner from non-profit Dialogue China, told the AFP news agency that Mr Kwon, 35, escaped.

For publicly criticizing President Xi, Mr Kwon spent time in prison in China.

Attempting to leave China by regular travel routes in order to claim asylum is highly likely to have caused him problems, and he is likely to have been subjected to an exit ban.

He said: “While [Mr Kwon’s means of entry into South Korea in violation of the law were wrong, his life-risking crossing into South Korea was motivated by the surveillance of the Chinese authorities and political persecution of Kwon since 2016.”

Mr Kwon is now considering whether to apply for refugee status in South Korea – which grants only a handful of requests each year – or a third country.