Binance, the world's largest crypto exchange, said a security breach had resulted in an estimated $US6.3 billion ($A9 billion) impact and it had worked with partners to freeze the affected assets.
About $US3 billion ($A4.3 billion) had been located so far, it said, giving no update on the status of the remaining $US3.3 billion ($A4.7 billion) as Binance co-founder Yi He said the company would cover "all hacking losses".
US blockchain analysis firm TRM Labs said the attacker did most of the raid in about 20 minutes.
"TRM attributes the attack to TraderTraitor, North Korea's elite hacking unit, based on robust on and off-chain intelligence," TRM said in a blog post.
"We make this judgment with high confidence."
In a statement, Binance said it was conducting security checks, its teams were "working around the clock" to resolve the issue and withdrawals would resume once the problem was fully resolved.
Binance co-founder Changpeng Zhao, who no longer runs the company, said in a social media post the incident "looked like a hack."
The exchange also temporarily suspended trading on its Binance Alpha platform as a precaution.
"Our security teams are reviewing all relevant information with urgency, and we will provide updates through official Binance channels as soon as we have verified information," it said.
Stablecoin providers Tether and Circle each said they responded to the incident by freezing funds - more than $US1.5 billion ($A2.1 billion) and more than $US800 million ($A1.1 billion), respectively.
According to analytics firm Chainalysis and other industry experts, it may be the world's biggest crypto heist.
The security breach was likely to have wider ramifications for crypto, which had already been under pressure lately due to higher US interest rates and softer demand from exchange-traded fund buyers, analysts said.
"It may further dampen risk appetite and prompt investors to reassess the safety of assets held on centralised exchanges, as well as counterparty, solvency and liquidity risks," HashKey Group senior researcher Tim Sun said.
Zhao pleaded guilty in 2023 to a felony related to his failure to prevent money laundering on the Binance platform and stepped down as chief executive.
US President Donald Trump pardoned him in 2025.
with Reuters
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