Blockchain site Poly Network said hackers had exploited a vulnerability in its system and taken thousands of digital tokens such as Ether.
In a letter posted on Twitter, it urged the thieves to “establish communication and return the hacked assets”.
In scale, the hack is on par with huge recent breaches at exchanges such as Coincheck and Mt Gox.
In its letter Poly Network said: The amount of money you have hacked is one of the biggest in defi [decentralised finance] history.
Law enforcement in any country will regard this as a major economic crime and you will be pursued.
“The money you stole are [sic] from tens of thousands of crypto community members, hence the people.”
We lost our life savings in a cryptocurrency scam'
EU plans to make Bitcoin transfers more traceable
Poly Network said a preliminary investigation found a hacker exploited a “vulnerability between contract calls”.
It urged various exchanges to block deposits of the coins, after millions of dollars in tokens were transferred to separate cryptocurrency wallets.
About $267m of Ether currency has been taken, $252m of Binance coins and roughly $85 million in USDC tokens.
Changpeng Zhao, chief executive of Binance, said his firm was aware of the hack, but added there was only so much he could do.
He said the group was “co-ordinating with all our security partners to proactively help”. “There are no guarantees,” he added.
Poly Network is a decentralised finance - or Defi - provider, which allows users to transfer tokens tied to one blockchain to a different network.