Portuguese media say police have detained the head of the country's immigration service and several other senior officials in a corruption investigation centered on the granting of residence permits to investors from outside the European Union.

Portugal offers so-called "golden visas" to non-EU citizens who invest large amounts. Most are granted to Chinese who buy real estate. The 2-year-old program has brought investments totaling more than 1 billion euros ($1.2 billion).

Portugal's Attorney-General's office said in a statement that officials carried out more than 50 searches as part of the investigation Thursday.

A separate police statement said 11 people were taken into custody on suspicion of corruption, money-laundering, influence peddling and embezzlement.

Authorities declined to name those detained, but media reports said they included senior public officials.