When Mr Wei agreed to take a management role at a nickel smelting project in Indonesia's south-east Sulawesi early last year, his company promised that after six months of working seven days a week it would pay for him to return to his family in China's Jiangsu to spend a few days with them.

It did not happen.

Instead, as China all but cut itself off amid the Covid-19 pandemic, the 55-year-old said he continued working without a day off, earning 15,000 yuan (S$3,100) a month until he and 200 others quit in October in protest at the lack of holiday time.

Mr Wei, who would give only his family name because of concerns that he and his family would face retribution if he spoke publicly, said he paid his own way to Jakarta to wait for the company, Obsidian Stainless Steel (OSS) - a unit of China's Jiangsu Delong Nickel Industry and logistics firm Xiamen Xiangyu - to arrange health checks and flights home.

He has been living in an airport hotel since.

"We came to Indonesia to support the motherland's Belt and Road initiatives," Mr Wei told The Straits Times through an interpreter. "I just want to be allowed to fly home."

Rights activists say Mr Wei's predicament reflects the often harsh working conditions and treatment that many Chinese workers face toiling at Chinese-funded smelting plants, rail and other projects spanning Africa, Europe and Asia that have come to be known as the Belt and Road Initiative.

While it is not clear how many are stranded, an April report from US-based non-profit China Labour Watch reckons hundreds of thousands are stuck like Mr Wei, owing to strict testing requirements and too few flights, which make airfares unaffordable for workers desperate to hold onto savings they have put aside for a house or school fees.

China Labour Watch interviewed nearly two dozen Chinese workers stranded in countries such as Algeria, Saudi Arabia, Jordan and Indonesia, and uncovered reasons that included high fines to break contracts and because employers had confiscated passports.

Chinese workers languishing in the transit hotels around Jakarta's Soekarno-Hatta international airport often rebuff requests for interviews out of fear they would be singled out for retribution.

A review of WeChat messaging groups provided by three OSS workers now housed in two airport hotels suggests there are at least 51 Chinese workers trying to get home. The workers said the chat group has been discontinued at the urging of the Chinese embassy in Jakarta.

OSS did not respond to a request for comment written in Chinese, English and Indonesian that was hand delivered to its office in Jakarta. A call seeking comment from Jiangsu Delong Nickel was directed to a man who confirmed workers for the company were waiting in Jakarta for flights to China and that the workers were under the auspices of China's embassy in Jakarta.

The official said the workers were waiting in Jakarta because flights to China were unavailable. But an online search revealed that, though limited, direct flights from Jakarta to Shenzhen, Guangzhou and Fuzhou were available through early next month.

Requests for comment to Chinese embassy officials were also unsuccessful.

The long wait for the workers is taking its toll.

Mr Wang, 41, an office administrator from Shanghai, said he has considered taking his own life. Since he arrived at his hotel in late March, he has left his 27 sq m room only four times - all for Covid -19 testing.

Mr Wang - who asked not to reveal his real name - said the lengthy quarantine means that he and his family are burning through precious savings because he is not working.

Mr Wang has paid 30,000 yuan - amounting to three months' salary - as a deposit to OSS, a practice that Mr Li Qiang, director of China Labour Watch, said is aimed at ensuring acquiescence among workers.

"The workers are asked to pay a high deposit for the purposes of holding them hostage," he told The Straits Times.

The US$2 billion (S$2.65 billion) OSS stainless steel venture, which went into operation in Konawe, south-east Sulawesi last year, comprises the lion's share of Jiangsu Delong's first overseas foray into nickel smelting and steel production outside China. A neighbouring US$1 billion PT Virtue Dragon Nickel Industry (VDNI) smelter went into production in 2017.

In December, VDNI made news when it was forced to shut down temporarily after protesting workers calling for better pay and permanent contracts set fire to equipment.

Complicating the plight of many workers are China's strict Covid-19 diagnostic and antibody testing procedures that scan not only for current infection but also antibodies that can turn up signs of past exposure and potential that they may still be a carrier of the virus, according to Mr Li.

As for Mr Wang, a handwritten note in English on the results of his May 15 test confirmed that he was not contagious.

Even so, his agonising wait continues.

"I am a citizen of China," he said. "I don't understand why I can't go home."

• Additional reporting by Lina Miao in Beijing