Los Angeles: Federal agents raided about 20 locations in three Southern California counties early on Tuesday as part of an investigation targeting "birth tourism" schemes in which pregnant Chinese women travel to the United States on fraudulent visas so that their children will be born US citizens.

Search warrants were served at the homes of people federal authorities suspected of running the operations as well as at apartment complexes where pregnant women were allegedly being housed.

Federal agents raid the apartment complex in Orange County, California, where authorities say a birth tourism business charging pregnant women $US50,000 for lodging, food and transportation was operating. Credit:AP

According to charges laid on Tuesday, operators charged Chinese women tens of thousands of dollars for services that guided expectant mothers through obtaining tourist visas, coaching them on successfully making their way into the country and housing them for months as they awaited giving birth.

The raids represent a rare federal crackdown against a widespread practice of foreign nationals giving birth in the US.