Eleven people are being questioned by Serbian police after a television graphic appeared to predict a winning lottery number before it was drawn.
The incident happened on live TV, sparking claims of a fix and forcing the head of the lottery to resign.
During the broadcast the number 21 was shown on screen before it became the next ball pulled from the machine.
The Serbian State Lottery (DLS) said it was "pure coincidence", but prosecutors have launched an investigation.
Aleksandra Gudelj, the host of the draw, is among those being held by police, AFP reports.
The DLS said a "technical mistake" was to blame for the appearance of the number 21 on screen, as a 27 was drawn from the machine.
The next ball to emerge was a 21, but that was merely a coincidence, the company said.
Nobody won the €1m ($1.09m; £703,000) jackpot.
The national lottery, which is state-run, is hugely popular in Serbia, particularly among pensioners and the unemployed.
Police have seized the lottery machine, balls and computer software as part of the their investigation, according to local media reports.
Prime Minister Aleksandar Vucic said anyone involved in criminal activity would be "brought to justice".
"The path to prison is very short," he said.