"Tokyo 2020 understands that there have been large-scale purchases following the first wave of the Olympic ticket lottery applications from a large number of IDs registered with false personal information," the organisers said in a statement.
"About 30,000 fraudulent IDs were generated" during a first-round online lottery to secure tickets for the summer games, the statement said.
"Altogether, about 6,900 tickets for 150 sessions were purchased using these fraudulent IDs, with a face value of about 180 million yen."
There were no details on who is suspected of creating the fake identities to carry out the purchases, though local media reported that the organising committee suspected a specific group was behind the plan.
Organisers said they were consulting with police and "will continue to monitor illegal applications during the second lottery sale."
A first wave of Olympic tickets went on sale for Japanese residents only in May, with would-be spectators required to sign up online by creating a profile and choosing which seats they wanted a chance to buy in a lottery system.
Around 3.2 million tickets were sold in the first phase of sales, with a second phase organised in August for those who missed out the first time around.
Olympic tickets can only be resold through an official Tokyo 2020 resale site, and organisers warned that any tickets bought via other resellers would also be invalidated.
