Some Chinese attempting to make their way to Western countries pay middlemen known as “snakeheads” to facilitate the journey. It can cost about $50,000 to $60,000 to be smuggled into Europe and $70,000 to $80,000 for the United States, according to Sheldon Zhang, a professor at the University of Massachusetts Lowell who specializes in human smuggling involving Chinese.

“Frankly, I am just as shocked to learn that these dead migrants were Chinese nationals,” Dr. Zhang said in an email on Friday. “I thought the snakeheads would have learned by now, from the Dover incident in 2000, not to use the lorries to transport human beings.”

Many of those who died 19 years ago were economic migrants who came from Fujian province, where businesses in some towns offer “courier services” for people to send their children to the West.

In recent years, experts said, the main regions sending economic migrants have expanded to include the depressed northeastern provinces of Jilin, Liaoning and Heilongjiang and Wenzhou, a bustling coastal city in eastern Zhejiang Province.

“There are still a large number of people desperate to leave China and go overseas,” mainly because they think they can make more money, said Ko-lin Chin, a professor at the Rutgers School of Criminal Justice who has studied human smuggling in China.

“In the rural areas, there’s a competition going on to see who can build a bigger house,” he added, involving families receiving remittances from abroad. “If you go to the villages and you see a five- or six-story house, you will understand what this is all about.”

Ms. Hua, the Foreign Ministry spokeswoman, bristled when asked during a news conference about Chinese nationals wanting to make such an arduous trip despite the country’s economic progress.