Police said they would work with the NSW Crime Commission and they have the full support of the NRL.
Dozens of players, officials and members of the public are expected to be interviewed.
Earlier this year, the Organised Crime Squad confirmed it was investigating allegations of match-fixing in two NRL games from last year.
Those games were a round 16 game between the Manly Sea Eagles and the South Sydney Rabbitohs, and a round 24 match between Manly and the Parramatta Eels.
Last month, it was revealed an April 2016 game between Manly and the Parramatta Eels was also being investigated.
At the time, the NRL said it would "take whatever action is necessary to protect our game".
"Anyone convicted of match-fixing can expect to be banned for life but, at this stage, no-one has been charged and we should avoid jumping to conclusions."
Today, the NRL said it would "support and provide any assistance requested by the police investigation into match-fixing".
In a statement, NRL chief executive Todd Greenberg repeated that there was no place in rugby league for any person found to be involved in match-fixing.
"We are not going to pre-judge any person associated with the game while this process is under way," he said.
"But I repeat my earlier warning that if any person is convicted of match-fixing they will face a life ban from any involvement in rugby league.