Billionaire receives message about his abducted wife

A Norwegian billionaire, whose wife has allegedly been abducted, says he's received a message from someone "in control of her".

Svein Holden, a lawyer for real estate tycoon Tom Hagen, says the letter arrived on January 16 and while it indicates that someone was "in control of her", there is no proof of life.

Anne-Elisabeth Falkevik Hagen, who went missing on October 31, is allegedly being held for ransom.

The ransom letter is said to have arrived digitally.

Earlier this month authorities reported the kidnapping and the note, saying the woman was taken from the couple's home near the capital of Oslo.

The ransom is reportedly $2 billion Norwegian krone (approximately AUD $328 million).

Local media outlets have reported the ransom letter as saying the woman would be killed if the money is not paid.

Chief investigator Tommy Broeske said earlier threats in the note were "of a very serious character".

"Our main theory is that the victim was kidnapped by unidentified perpetrators at her home," Broeske said during a news conference.

He says the family have urged not to pay the ransom.

Norwegian authorities are working together with Europol and Interpol on the case.