Federal authorities began arresting more than 100 organised crime suspects on Thursday, the FBI said, in what NBC New York called the largest Mafia bust in New York history.
US Attorney General Eric Holder and other top officials were due to hold a news conference in Brooklyn later on Thursday to disclose details.
"Early this morning FBI agents along with our law enforcement partners began arresting over 100 organised crime members for various criminal charges," Diego Rodriguez, the FBI's special agent in charge in New York, said in a brief statement.
NBC New York, citing unnamed sources, said the FBI was calling it the biggest Mafia roundup in New York history and that it targeted all five of New York's Mafia "families" plus one in New Jersey.
The suspected gangsters would be charged with racketeering, murder and numerous other crimes in multiple indictments that will be unsealed in Brooklyn federal court, the New York Daily News reported.