Japanese cryptocurrency exchange Liquid says hackers have compromised some of its wallets and stolen more than $90 million.

The firm's operations and technology teams detected unauthorised access to "warm" wallets early Thursday. Warm wallets are based online.

Crooks took over $91 million in crypto assets, of which just over $16 million was frozen thanks to the efforts of other exchanges and the wider community, says Liquid.

Blockchain analytics outfit Elliptic has put the total losses at $97 million. This includes $45 million in Ethereum tokens, "which are being converted into Ether using decentralised exchanges," enabling "the hacker to avoid having these assets frozen".

Liquid is asking customers not to make crypto deposits into their wallets and has halted all crypto withdrawals. Fiat withdrawals and deposits are still available.

Concludes the statement: "Liquid will continue to do everything in its power to mitigate the impact from this incident and restore full service as soon as possible."

This is the second hack at Liquid in less than a year. In November, a malicious actor managed to change DNS records and gained access to document storage infrastructure. However, no funds were stolen.

Earlier this month, Poly Network saw $610 million in crypto stolen, only for the hacker to return the vast majority and receive the offer of a bug bounty.