Coincheck, Japan's largest cryptocurrency exchanges, revealed it has lost nearly $400 million in NEM tokens.

According to Bloomberg, the 500 million NEM tokens were sent "illicitly" outside the venue.

In a late-night press conference on Friday at Tokyo Stock Exchange, co-founder Yusuke Otsuka said they did not know how the tokens went missing, but they know where the funds were sent.

"We are tracing them and if we're able to continue tracking, it may be possible to recover them," he told the press, adding "But it is something we are investigating at the moment."

Since Jan. 27, Coincheck has already restricted deposits and withdrawals for NEM, saying there is no concrete timeframe yet when these activities would resume. The currency exchange, however, said users will still be able to log-in and access their dashboards.

NEM is the 10th largest cryptocurrency by market value. Following the theft, it fell 11 percent over a 24-hour period. It also affected other digital currencies, with Bitcoin falling by 3.4 percent and Ripple dropping by 9.9 percent.

This cryptocurrency theft is among the biggest losses of investor assets since Japan launched Bitcoin in 2009, kicking off the advent of digital currencies. It follows the collapse of Mt. Gox in 2014, which declared bankruptcy after hackers stole 850,000 Bitcoins, worth $460 million at that time.

Contrary to rumors, though, Coincheck does not plan to follow on Mt. Gox's footsteps. "Along with our ongoing efforts to file applications to be registered as a Cryptocurrency Exchange Services Agency, we will continue business," the company announced in an official statement, as reported by Cointelegraph. 

Japan's Financial Services Agency is already looking into the incident.

On Saturday, Coincheck announced it will issue a full refund to the 260,000 users that were affected by the NEM hack. The company said each NEM coin lost will be valued at 88.549 Japanese Yen, which is NEM's weighted average before trading was halted due to the hack.