The police statement late on Tuesday came after Gyula Balasy, the owner of several top media companies that have designed government campaigns for Orban for more than a decade, said he offered to hand over his firms and some of his investments to the state as the new government of Peter Magyar takes over.
Balasy said he had offered his companies to the state "not because I have something to hide or because we have done something unlawful or wrong".
He said the accounts of several of his companies had been frozen on April 27.
Balasy's Lounge Group did not immediately respond to an emailed Reuters request for comment.
Magyar, whose centre-right Tisza party ousted Orban after 16 years in an election in April, will take his oath on May 9 as prime minister.
He has pledged to clamp down on corruption and "reacquire stolen state assets".
On April 28 Magyar said that tax authorities in Hungary had blocked transfers of funds abroad by unidentified people linked to a top aide to Orban.
Police said on Tuesday that based on information from the tax authority NAV's special unit, an investigation has been launched because of misappropriation and money laundering "against an unknown perpetrator".
"These proceedings include a probe into issues related to the events organising group of companies, which was revealed by the managing director himself in the press," police said, referring to an interview that Balasy gave to news site Kontroll late on Monday.
"During the investigation, funds have been seized and accounts have been frozen."
Police said they also launched a separate investigation into the same group of companies "with relation to overpriced contracts on suspicion of misappropriation of funds against an unknown perpetrator".
Balasy's firms designed Orban's anti-Ukraine election campaign, which framed the April vote as a choice between war and peace and, among many others, his anti-immigration campaigns in the past, winning hundreds of contracts from Orban's National Communications Office.
Transparency International has said that in the 2019-21 period alone, Balasy's companies Lounge Design, New Land Media and Media Dynamics won a total of 295 billion forints ($A1.3 billion) worth of state contracts mostly from the National Communications Office, which was in charge of Orban's campaigns and was key to winning past elections.
