Six raiders dressed as policemen robbed the headquarters of Greek ferry company ANEK in Piraeus late on Sunday.
The armed assailants immobilised ANEK staff and then escaped with an unquantified amount of money, the state-run Athens News Agency reported.
ANEK, which is listed on the Athens Stock Exchange (ASE), did not file any notification on the incident to bourse authorities by early Monday.
However, Greek media cites a statement saying that all employees that happened to be at work during the heist at its Akti Kondyli offices on Sunday were “healthy and safe”.
ANEK is cooperating closely with police in their manhunt to nab the perpetrators, it added.
The company has eight ships and a market capitalisation of about €20.5m ($23.4m) on the ASE as of 7 February.
ANEK stock has been trading for years in a restricted, supervised manner, given the company’s fragile financial position.
The company was reported in October to be exploring a merger with the Attica Group, a much bigger local rival. However, nothing of the sort has materialised yet.
ANEK made international headlines in December 2014 when one of its chartered ferries — the 26,900-gt Norman Atlantic (built 2009) — went up in flames in the Adriatic Sea, causing the deaths of at least 12 people.
Top company officials were convicted over the incident last year but they immediately appealed the decision and were released pending a new trial in Greece, which will examine the case from scratch.