Norwegian police are investigating the 'strange' disappearance of a cyber security expert who is friends with Julian Assange.

Arjen Kamphuis, 47, has been missing since August 20 when he left his hotel in the northern Norwegian town of Bodo.

He was due to fly home to Amsterdam two days later but never made his flight.

Assange's organisation WikiLeaks tweeted on Saturday about the Dutchman's disappearance, sparking numerous conspiracy theories online.

Arjen Kamphuis, 47, has been missing since August 20 when he left his hotel in the northern Norwegian town of Bodo

Assange's organisation WikiLeaks tweeted on Saturday about the disappearance, sparking numerous conspiracy theories. Pictured: A missing poster

Many speculated that his disappearance has something to do with his ties to Wikileaks, an international non-profit organisation that publishes secret information.

But others noted he was a keen hiker and said he could simply be lost in the woods.

Wikileaks said that Kamphuis had a ticket for a flight departing on August 22 from Trondheim, a city located more than 700 kilometres (435 miles) south of Bodo.

'The train between the two takes (approximately) 10 hours, suggesting he disappeared either in Bodo, Trondheim or on the train,' the organisation tweeted.

Kamphuis is best known for his book titled Information Security for Journalists, which gives writers tips on how to keep their work safe from spying.

A website set up to gather information says: 'He is 47 years old, 1.78 meters tall and has a normal posture. He was usually dressed in black and carrying his black backpack. He is an avid hiker.'

Many speculated that his disappearance has something to do with his ties to Wikileaks, an international non-profit organisation that publishes secret information. Pictured: Arjen Kamphuis

'We have started an investigation,' said police spokesman Tommy Bech, adding that so far they had no clue about the Dutchman's whereabouts.

The police 'would not speculate about what may have happened to him,' Bech said.

Assange has been holed up at Ecuador's embassy in London since 2012 when he was granted political asylum as he feared extradition to the United States to face trial over WikiLeaks' publication of secret US military documents and diplomatic cables in 2010.