4,502.9 BTC ($305 million) was stolen from the exchange.
DMM Bitcoin said it will guarantee the full amount stolen.
All spot buys have been temporarily restricted and customers withdrawing yen may face delays.
DMM Bitcoin, a Japanese cryptocurrency exchange, said it lost 48 billion yen ($305 million) of bitcoin {{BTC}} following a hack.
In a blog post on its website, DMM Bitcoin said 4,502.9 BTC "leaked" out of the exchange. Measures have been taken to avoid further unauthorized outflows.
"Please be assured that we will procure the equivalent amount of BTC equivalent to the outflow with the support of the group companies and guarantee the full amount," DMM Bitcoin said.
The exchange has restricted all spot buys on the platform and added that Japanese yen withdrawals "may take more time than usual."
The loss marks the second largest in the region. Coincheck was hacked for 58 billion yen in 2018.