Once family and friends have scraped together enough money, the odyssey may begin with a trip to China to pick up forged travel documents. That is how many of the dozens of people who died in the truck began their journey, said Anthony Dang Huu Nam, a Catholic priest serving a church in the town of Yen Thanh, where he said dozens of the victims were from.

On the way from China to Russia to Western Europe, one of the most punishing stretches is the walk through Belarusian forests to the Polish border. In a 2017 French survey of Vietnamese migrants, a man identified as Anh, 24, told researchers that he and five other men, led by a smuggler, were repeatedly arrested in Belarus, only to be released at the Russian border to try again. When they finally succeeded, they were met by a truck waiting on the Polish side.

“We were cold,” the survey quoted him as saying. “We didn’t eat anything for two days. We drank water from melted snow.”

Other routes, choreographed down to the minute, land migrants in European airports with recycled visas and travel documents, according to “Precarious Journeys,” a recent report from ECPAT, an anti-child-trafficking organization, and other groups. As a precaution, smugglers in Vietnam often tell people to arrive at airport check-in desks 10 minutes before they close, for instance, so agents do not have enough time to inspect paperwork.

The trip can take months, even years. Nguyen Dinh Luong, 20, one of the migrants believed to have died last week, wanted to go to France to find work and support his siblings, seven of them in all, his father, Nguyen Dinh Gia, said. But in Russia, he overstayed his tourist visa and was confined to his house for six months. Then he moved to Ukraine and France, where he found a job as a waiter, before deciding to go to Britain for work in a nail salon.