Officers made the detentions on prosecutors' orders and also seized luxury cars, watches, jewellery and a substantial amount of cash, Anna Adamiak, spokeswoman for the National Public Prosecutor's Office, told reporters.
"Today's activities involving those detained in the Zondacrypto case have been completed," she said in the evening. "We will provide information about further activities on Thursday."
Stock market investor Rafał Zaorski was brought to the Katowice branch of the National Public Prosecutor's Office on Wednesday afternoon in connection with the investigation, state news agency PAP reported.
Media reports have linked him to missing businessman Sylwester Suszek and his cryptocurrency exchange BitBay, which operated before Zondacrypto.
Zaorski told reporters: "I am the victim."
Two other people were also detained, identified only as Jaromira W. and Anna P., according to Polish news outlet onet.pl.
Jaromira W. is the former wife of Marian W., known as "Maniek," the main suspect in the disappearance of Suszek, the founder of BitBay.
Anna P. was a close associate of Marian W., according to onet.pl.
Justice Minister and Prosecutor-General Waldemar Żurek said investigators were looking for "various pieces of evidence," including documentation.
He told a news conference that prosecutors would be able to outline their next steps after questioning those detained.
The investigation into Zondacrypto was opened by the District Prosecutor's Office in the southern city of Katowice on April 17 on suspicion of large-scale fraud and money laundering.
Several thousand criminal complaints have been filed in the case, prosecutors said.
In early August, the Zondacrypto investigation was merged with a separate case concerning the March 2022 disappearance of Suszek.
Polish Olympic Committee (PKOl) chief Radosław Piesiewicz was detained last Thursday as part of the investigation.
That same day, prosecutors charged him with influence peddling and with favouring a group of Zondacrypto creditors to the detriment of others amid concerns over the company's insolvency.
Piesiewicz denies the charges.
After questioning Piesiewicz, prosecutors asked a court to order his detention for three months, and the court granted the request.
On Monday, Mieczysław Nowicki, one of Piesiewicz's deputies, called a meeting of the committee's executive board for September 8.
It will be the first meeting of the PKOl leadership since Piesiewicz was detained.
However, a majority of the 16 other members of the body are also calling for a full board meeting, arguing that only the full board has the authority to formally remove Piesiewicz during his term.
No decision has yet been made on whether to convene such a meeting, according to PAP.
Zondacrypto became the Polish Olympic Committee's general sponsor in October last year. In April, Piesiewicz said the PKOl would terminate the sponsorship agreement due to payment defaults.
On April 30, the committee decided to terminate the sponsorship and remove the sponsor's illuminated sign from its Warsaw headquarters.
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Source: TVP Info, IAR/PAP