Cryptopia has pulled its website and services offline, citing a "security breach" resulting in "significant losses."
At the time of writing, the cryptocurrency exchange, based in New Zealand, is offline and a message posted to the home page says the domain is in "unscheduled maintenance mode."
Cryptopia said on Twitter that a security incident took place on Monday. Once this was detected by staff, services were pulled to "assess damages."
Trading is suspended until further notice.
"We are committed to getting this resolved as quickly as possible and will keep you all updated every step of the way," Cryptopia added.
New Zealand's police force and the High Tech Crimes Unit are now investigating.
In a statement provided by the New Zealand police, law enforcement says it was informed of "unauthorized transaction activity" taking place at the cryptocurrency exchange, and "a dedicated investigation team is being established in Christchurch including specialist police staff with expertise in this area."
Meanwhile, alerts from Whale Security suggest that a number of unusual transactions took place over the weekend. The first transaction involved 48,029,306 Centrality (CENNZ) tokens, worth roughly $1.2 million being transferred from Cryptopia to an unknown address, alongside 19,391 Ethereum (ETH), worth $2.4 million.
It has not, however, been confirmed that these transactions are connected to the reported security incident.
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The transactions are also being monitored by the founder of Validity Samuel Gosling, as outlined in this thread concerning the firm's reported hot wallet.
Little is known at present as to the cause, individuals potentially behind the breach, or how much was lost. However, we are likely to find out more in the coming days.
ZDNet has reached out to Cryptopia with additional queries and will update if we hear back.