Ly Bao Son, 43, and Vuong Nguy, 39, were in a car in Quang Ninh Province when border guards stopped them on Tuesday, according to a report on the province's news website.

One of them was holding the infant, but neither could prove it was related to them when asked by border officials.

They then confessed that Son was a middleman, and Nguy had hired him to get Le Ngoc Hieu, a Vietnamese woman, to act as a surrogate mother and deliver a child for 150,000 Chinese yuan ($21,500).

Vietnam legalized surrogacy in 2015 but only to benefit infertile couples and only by family members. Commercial surrogacy is punishable by up to five years' imprisonment.

The child was born in Ho Chi Minh City.

The officials transferred him to a local medical center where he is in normal health.

Authorities are looking for his mother.

China is a major trafficking destination of Vietnamese women and girls. Baby victims have been reported more recently.

In August a 21-year-old Vietnamese woman was arrested in Lang Son Province while trying to cross into China with a newborn baby.

She told the police she was taking the infant to Fujian Province in China and would be paid VND15 million ($650).

A month before that border guards detained a couple who were allegedly taking a 14-day-old baby to China for sale.