Police arrested the head of Portugal's immigration and border service as part of an investigation into corruption linked to the issuing of so-called "golden visas" to wealthy foreign investors.

The Prosecutor General's office said several arrests were made and searches carried out in different locations across Portugal as part of the investigation into the visas and other matters on suspicion of corruption, influence peddling and money-laundering.

The official Lusa news agency said Manuel Palos, head of the SEF immigration service, was one of those detained and SEF premises were searched. A police source, who did not want to be identified, confirmed the detention to Reuters but would not say if Palos was being charged with any crime.

The golden visa programme was launched by the government in late 2012 during a debt crisis and gave residency permits to non-EU citizens who invested in real estate. It has brought in more than one billion euros in much-needed investment since, mainly from Chinese buyers of property willing to invest more than 500,000 euros in real estate in Portugal.

Neighbouring Spain and some other EU countries have similar programmes.  The Portuguese permits allow foreigners to travel freely within Europe's 26-country Schengen zone without restriction.

Opposition politicians have long argued that the scheme may open way to criminals and stoke corruption. The government insisted that its checks of the applicants meet all EU standards, but in June acknowledged that it was investigating corruption allegations linked to the programme.

Portugal has issued golden visas to around 1,500 people, most of them Chinese, as well as citizens of Russia, Brazil, Angola and other countries.