Police and government officials have launched an investigation into an unprecedented scandal involving the sale of Norwegian visas and residence permits.

The government is severely embarrassed by the affair - particularly as immigration issues are likely to figure prominently in local and regional elections in September.

The racket is reported to have been flourishing for more than 10 years, involving civil servants at home as well as embassy and consular staff in at least five countries.

There are no reliable estimates at this stage of how many people might have entered the country with false papers.

In one developing country, the going rate for a residence permit is said to be $8,000; in another, Norwegian passports are freely available on the black market for as little as $2,500.

According to one witness - himself an immigrant - half the people he knows in Norway have, as he puts it, bought their way in.

Worse still, the trade in false papers appears to have been known to the government all along.

Several prosecutions have been blocked, presumably on orders from the highest political level, despite apparently ironclad police evidence.

Although Norway's near-xenophobic attitude to immigrants has been changing slowly in recent years, the extreme right-wing and rabidly anti-immigrant Progress Party is still the second-largest in the country.