Shortly after the man was overpowered, police special forces combed the building for explosives and declared it safe at about 21:00 GMT, police spokesman Christine Scholts said.
"We are currently investigating who this man is and what he wants," she said.
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Prosecutors, for their part, said that the man, who is reportedly from the Dutch town of Pijnacker, is being held on suspicion of making a threat, illegal possession of a gun and taking a hostage.
His motive remains unclear, Dutch media reported, adding that he was believed to be a student at Delft Technical University and had recently lost his parents.
The NOS footage showed the man saying: "The things that are going to be said [pause] — those are very large world affairs. We were hired by the security service."
According to the AP, a reporter speaking to the man said that he had claimed to be from a "hackers' collective."
Earlier, Hilversum mayor Pieter Broertjes said that additional security measures had been taken to protect media workers after gunmen killed 12 people at the Paris offices of French satirical weekly Charlie Hebdo earlier in January.