Hackers stole around 100 million dollars in cryptocurrency from a blockchain bridge developed by Harmony.
The start-up reportedly notified other exchanges and stopped its bridge, called Horizon, while launching investigations into the theft.
One individual account is thought to be behind the heist.
The company is reportedly working with national authorities and forensic specialists, including the FBI, to identify the culprit and retrieve the stolen funds.
There's already been a series of similar attacks on blockchain bridges.
Bridges, which allow users to transfer tokens from one blockchain to another, have become a key target for hackers due to vulnerabilities in underlying code.
Prior to this incident, more than 1 billion has been looted in crypto so far this year.