A 60-year-old man in Singapore has been allowed by his wife to take young Vietnamese brides but only on the condition that she gets to watch their "child-making process", reported China Press.

The condition had so far scared off three young Vietnamese women recommended by a bride agency to the couple.

The daily quoted the agency's owner, Marco Lim, as saying that in the past several years, he had recommended women to the couple, the latest being a few months ago.

"The childless couple approached my agency and shortlisted the candidates. Each woman tried to live with them but the first two did not even make it past two weeks.

"They left and returned to Vietnam," he said, adding that the third woman, a 25-year-old, stayed for three months.

Lim said he only found out about the reason behind the failed relationships after he coaxed the women into telling him the truth.

"They must have felt pressured because the wife would watch them carefully each time they had sex with the man. I was told that the wife would even set the schedule for the man to have sex with the women.

"She also held on to their passports and forbade them from making calls," he said.