Norway's police said Wednesday the missing wife of one of Norway's richest men has been abducted, and that her suspected kidnappers have demanded a ransom.

According to local newspaper VG, 68-year old Anne-Elisabeth Falkevik Hagen, the wife of Norwegian businessman Tom Hagen, has been missing for ten weeks, since October 31st of last year.

A ransom of €9 million (S$14 million) in cryptocurrency has been demanded for her release, VG said.

"Our main theory is that the victim was kidnapped by unidentified perpetrators at her home" in Lørenskog, about 12 miles (20km) from Oslo, he said, adding that police had from the beginning examined several possible theories about her disappearance.

Due to the sensitivity of the operation, the police have been forced to keep an extremely low profile while investigating the case.

The cautious nature of the remarks could be an indication that police have not received proof that Hagen was indeed being held by the people demanding the ransom. Broeske said they were working with Europol and Interpol on the case.

Norwegian tabloid Verdens Gang, quoting unnamed sources, reported that a ransom demand corresponding to €9m had been made, payable in the Monero cryptocurrency.

This has reportedly prevented the police from searching for the kidnappers as aggressively as they would normally have done, while also limiting their ability to gather evidence in the vicinity of the couple's residence outside of Oslo.

"The reason for us to go public with this case now is that despite a broad and extensive investigation, we need more information", Broeske told a news conference.

The missing woman's husband, Tom Hagen, is listed as the 172nd wealthiest person in Norway, with a net worth of 1.7 billion kroner, or about United States dollars 200 million.

A real estate investor, he owns 70 per cent of electricity company Elkraft which he co-founded in 1992, Norwegian media reported.