The cost blow out was caused by unexpected payments for building lanes on highways, as well as rising materials costs and personnel expenses, said NHK.
The Tokyo 2020 Organising Committee will be able to raise only about 450 billion yen from sponsors and ticket sales, which means a shortfall of more than 1 trillion yen, the report said.
The committee had earlier estimated a cost of 300 billion yen for the Summer Games in 2020, but that was optimistic, said NHK.
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Total costs for staging the Tokyo Olympics, estimated to be more than 2.1 trillion yen, will be shared by the committee, the Tokyo government and national government.
(Reporting by Junko Fujita; Editing by Michael Perry)
