A lottery for single Chinese men seeking brides in Vietnam is a sheer publicity stunt, an expert said, as the Foreign Ministry issued cautions about similar activities.

More than 20,000 people have registered to win a trip to Vietnam offered by group-buying website 55tuan.com before Singles' Day on Monday, a website representative said. One will have the chance to have his trip reimbursed if he finds a bride there.

A customer service staff member said: "Our activity is free for registration. However, only one person can get this chance by lottery, and then our staff will inform the lucky person about arrangements for a blind date in Vietnam."

She added that the winner needs to present a certificate proving his single status and his travel expenses could be reimbursed if he later shows a foreign marriage certificate.

Li Ying, vice-president of the law school at China Women's University, told China Daily she didn't agree with such activity. "The way of group-buying Vietnam brides is degrading to women, not showing respect to them, but regarding them as property."

"It seems that this activity is a stunt, the purpose of which is to attract people's attention," Li said, adding such marriages are full of risk for the foreign brides and that related laws and regulations in China and Vietnam also differ.

"Marriage should be built on affection, not on material possessions," Li said. "A marriage can last a long time with real emotion."

In a statement issued on its website on Saturday, the Ministry of Foreign Affairs asked Chinese citizens to be cautious about information on overseas dating and to research the related laws, regulations and the qualifications of intermediaries before they go abroad.

In recent years, some Chinese have trusted false information online and been cheated when they went to Vietnam for blind dates, it said.