A gang that allegedly charged Chinese citizens up to €50,000 (£43,000) to enter Europe and the US, and which is thought to have fuelled the illegal sex trade in the West, has been broken up following a joint Spanish and French police operation.

More than 70 suspected people-traffickers were arrested after a two-year investigation into the network. Spain's Interior Ministry said that two central figures at the European end of the operation, reportedly based in Barcelona, were among the 51 arrested in Spain and 24 in France.

Officials alleged that in return for thousands of pounds, the smugglers would provide false passports and other necessary permits to leave China and enter Europe or the US.

Chinese nationals were ferried to destinations including Britain, Spain, France, Greece, Italy, Turkey and the US. Those who could not afford to pay were locked into repayment schemes that often saw them end up in prostitution, investigators said.

The extent of the people-smugglers' association with Chinese organised crime has not been revealed by prosecutors. They claimed yesterday that "employees" of the organisation would provide safe houses for the Chinese "passengers", while false documents were prepared, usually for entry to the UK or US. The group "pinned" or shadowed the migrants throughout their journey. This was said to have been undertaken by fully trusted members of the gang who had in-depth knowledge of airports and cities on the transfer run.

It is claimed that organisers constantly altered the routes and documents used to move people based on the success or failure of previous trips, in order to better avoid detection of their charges.

The transportees were given instructions on how to pass unnoticed at border controls and were advised to camouflage themselves among tour groups, investigators said.

They added that a total of 81 false passports from countries including Taiwan, Korea, Malaysia, Japan, Hong Kong and Singapore were seized. All the counterfeits had been produced in China.

Spanish and French authorities also seized materials used for forgery such as laptops, scanners, UV lamps, rubber stamps and ink pads, as well as 11 telephone terminals, cash and other documentation.

The total number of people to have been smuggled from China remains unconfirmed.

The gang's main European hub is thought to have been Barcelona's Prat de Llobregat airport, with the city acting as a springboard to the passengers' final destinations.

According to the Interior Ministry, in 2011 an investigation was launched into the complex operation "dedicated to aiding and abetting illegal immigration and tangentially to human trafficking for purposes of sexual exploitation".

The smuggling organisation is said to have been well structured and hierarchical, with its chief based in China and established independent cells operating in different countries with "the greatest secrecy".

The EU and US have come to recognise that human-trafficking through Spain is an increasing problem, but Spain has been taking more measures to protect people, particularly women and children. In March, Spanish police uncovered two prostitution rings in Madrid that were being run by Romanians.

Elsewhere, six migrants drowned yesterday after their boat ran aground on a sand bar off a popular Sicilian beach and they tried unsuccessfully to swim to shore. About 90 others on board survived, authorities said.