Scores of people have been arrested in Spain and France in a crackdown on a gang smuggling Chinese nationals into Europe and the United States.

Spanish police said on Saturday that 51 people had been arrested in Spain, with another 24 arrests were reported in France, following a two-year joint investigation.

The bosses of the operation were arrested in Barcelona.

The Spanish interior ministry said the gang charged up to $66,700 to transport mainly Chinese and Malaysian nationals to the US, Britain, Spain, France, Greece, Italy and Turkey. Some of the people trafficked ended up in the sex trade, the ministry said.

The gang's main European hub was Barcelona airport. It allegedly used the city as a stopping-off point for Chinese while false documents were prepared.

A total of 81 false passports from South Korea, Taiwan, Malaysia and Japan were recovered in raids, as well as fake immigration stamps, Chinese and European currencies, and weapons including a handgun.

"The composition of this perfectly structured, hierarchical organisation, with its kingpin in China and independent cells operating in different countries, completely shut off from each other, complicated the investigation," the police statement said.

The traffickers accompanied their clients all the way from China to Spain - the last stop to the final destination, usually the United Kingdom or the United States, it said.

The route taken from China, as well as the travel documents used, "changed constantly according to the successes and failures of previous trips... or in order to prevent discovery of the traffickers."