US investigators launched dawn raids Tuesday on dozens of locations dotted around Los Angeles suspected of offering "maternity tourism" services for Chinese mothers wanting to give birth to gain citizenship for their children.

Mothers pay over $50,000 for packages allowing them to give birth in the United States, which confers US citizenship on their offspring, the Immigration and Customs Enforcement (ICE) agency said.

The businesses -- advertised online and which sometimes offer trips to Disneyland as part of packages -- had names including "You Win USA Vacation Resort" and "USA Happy Baby Inc."

"Such businesses provide travel and lodging services to pregnant foreign nationals interested in coming to the United States to give birth so their offspring will be American citizens," ICE spokeswoman Virginia Kice said.

When babies born in the US reach adulthood they can apply for visas for family members living abroad, ICE noted.

Kice said the raids, in three dozen locations overall, aimed to gather "further evidence related to a variety of possible criminal violations, including visa and tax fraud, money laundering, and conspiracy."

According to ICE, the maternity tourism businesses cater mostly to Chinese women who pay $15,000-$50,000 for the services, which can include getting social security numbers and US passports for their offspring.

Kice added that investigators alleged that "the operators of the maternity tourism businesses coached clients to misrepresent the purpose of their visit in order to obtain tourist visas to enter the US."

"Business operators also instructed clients to wear loose clothing on their inbound flights and not carry baby paraphernalia in their luggage to avoid arousing suspicion when being inspected" by US customs officers.

The fees cover lodging, transportation, and food, but do not include medical care. The women appear to pay cash for pre-natal visits and the actual delivery.

The more expensive maternity tourism packages included recreational activities such as visits to Disneyland, shopping malls, even an outing to a firing range.

- 'Mother group' -

There is nothing in US law that makes it illegal for pregnant women to enter the United States and nobody was arrested in the raids.

But if a pregnant woman or anyone else uses fraud or deception to obtain a visa or gain admission to the United States, "that would constitute a criminal act," said an ICE spokeswoman.

"Likewise, that would also be true if someone conspires with others who then commit fraud on his or her behalf."

In an affidavit which formed part of the investigation, police recounted receiving an "anonymous tip letter" about a man named Chen, who it said was in a sham marriage to a woman called Zhu in Irvine, south of Los Angeles.

"Chen was operating a 'mother group'.. utilizing approximately 10 units within the apartment complex," it said.

"Pregnant foreign nationals paid Chen between $36,745 and $52,721 to enter the United States as tourists, reside in his units, and give birth to children."

The ICE-led raids -- on apartment complexes in the Irvine, Rancho Cucamonga, Rowland Heights and Walnut districts outside LA -- were helped by other agencies including the Internal Revenue Service, US Customs and Border Protection.