China's Foreign Ministry issued a notice on Saturday asking Chinese citizens to stay alert to "matchmaking services" after some people recently lost money on "bride-seeking" trips to Vietnam promised by some Internet firms.

"The Center for Consular Assistance and Protection would like to remind all Chinese citizens to treat foreign matchmaking information with caution. Citizens should study relevant regulations both domestic and foreign, and carefully examine the qualification of the matchmaking agencies before embarking on a trip," the notice said.

In recent times, "bride-order" businesses to Vietnam have become popular with those Chinese men who are unable to find a suitable match at home and are lured by the prospects of "bargain brides" found through such services.

With November 11 being observed as the "Singles' Day" in parts of the world, service providers such as 55tuan.com claimed to offer free trips to Vietnam in pursuit of "true love." Launched on November 6, the website boasted of over 20,000 participants as of Sunday.

Zhang, an agent with a lone name, from Southwest China's Yunnan Province, told the Global Times that her agency organizes tours to Vietnam and arranges blind dates for single Chinese men.

Such dates typically take a month to be scheduled and could cost some 60,000 yuan ($9,851) in commissions to an agency. In return, the men get to bring home a "gentle and beautiful" Vietnamese woman, Zhang said. The fee only covers the expense for transportation and accommodation, she added.

"You will have to pay another 10,000 yuan as gifts to the bride's family. The cost will be much more if you select a prettier bride," she said.

Zhao Yongjiu, a marriage counselor at Love Wisdom, China's first "love and marriage" tutoring company, told the Global Times that the gender imbalance may have helped the business grow with men outnumbering women in villages while there are more single women in cities.

According to Qi Huan, a research fellow with the Institute of Southeast Asian Studies at the Yunnan Academy of Social Sciences, the agencies have been active in China for decades.

"The Vietnam War compounded poverty in the country and sparked a serious gender imbalance. There are many women who seek husbands from wealthier countries," Qi told the Global Times previously, adding that many Vietnamese women marry men from Guangxi, Yunnan, Zhejiang and Fujian.

Tan Fang, a professor with the East China University of Political Science and Law, warned that many a times Vietnamese women are forced to leave their homes without legal marriage licenses and end up being trafficked.

In November 2011, police in North China's Hebei Province rescued 206 foreign women who were illegally "bought" by single men.

Similar cases were reported from Jiangxi Province in 2010, when at least 20 Vietnamese brides ran away from their Chinese "husbands," according to news portal chinanews.com.