Madrid, Spain - A prominent digital tech entrepreneur says thieves made off with "several dozen million" in bitcoin after robbing his apartment.

The heist took place on Tuesday in a luxury apartment complex near the Prado Museum in the center of the Spanish capital of Madrid.

The victim is reported to be Zaryn Dentzel, a 38-year-old US citizen from Santa Barbara, California who has lived in Spain since the late 1990s.

He is the co-founder of Tuenti, a Spanish social network-turned communications company once called "the Spanish Facebook", and is said to be a Bitcoin millionaire.

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Dentzel said the robbers tortured him for four hours, forcing him to reveal the passwords for his digital assets.

Four or five people rang the man's doorbell and forced entry when he opened the door, covering his security cameras.

Two other men - a friend and a handyman - were in the apartment at the time of the robbery, according to the victim's statement. Both of them were reportedly bound and gagged.

Dentzel said the thieves attacked him with a taser, carved into his chest with a knife, and sprayed something in his eyes while tying him up. Laptops, tablets and mobile phones are said to have been taken.

Spanish police confirmed the accuracy of the events. The criminals are suspected to have come from Eastern Europe, however investigators are pursuing all possible avenues, a spokesperson said.

According to media reports, there are witnesses to the crime. One neighbor reportedly said that he saw a group of men, faces covered, carrying several large bags as they left the building.

The investigation is still ongoing.