From the outside, they were typical Southern Californian townhouses with bright white walls and Spanish tile roofs.

But inside, a new kind of international business thrived -– maternity wards for wealthy expectant mothers from across the Pacific.

For a fee, Chinese women received room and board and a chance to deliver their babies in the United States and become mothers to instant U.S. citizens.

Southern California has become a hub for this growing phenomenon, known as birthing tourism.

One such business was busted earlier this month when code enforcement officials from the city of San Gabriel responded to a complaint about noise and an unusual number of pregnant women in a quiet Palm Avenue neighborhood.

When officials went to the location, they found about 10 mothers and seven newborns living in three townhouses that had been illegally converted into maternity wards.

"The people were sitting and eating at a table, all the babies were in bassinets with a nurse attending to them," said Jennifer Davis, community development director for the city of San Gabriel.