Greece said that final bids for a majority stake in Piraeus Port Authority, operator of its biggest port, were submitted on Monday but the prospective buyers will not be made public until early next month.
Alexis Tsipras's government had halted the sale after winning elections in January but resumed the process under the 86 billion-euro bailout deal it agreed with its euro zone partners in the summer.
The deadline for final bids was 1700 GMT on Monday.
"The procedure for the submission of binding offers for Piraeus Port Authority was completed today," the country's privatisation agency (HRADF) said in a statement.
The agency said there will be an announcement on Jan. 12 when the bids will be unsealed.
A senior HRADF official said earlier on Monday: "We will delay the opening because of the (Christmas) holidays, which means it will be around Jan. 10."
Greece has said that China's Cosco Group, Denmark's container terminal operator APM Terminals and Philippines-based International Container Terminal Services were interested in the sale.
A 51 percent stake in the port is up for sale, down from an original 67 percent and leaving the government with 23 percent. Would-be buyers may opt to acquire an additional 16 percent stake over five years after completing mandatory investments of about 300 million euros.
Athens repeatedly postponed the submission of binding bids after changing some of the terms of the concession in an effort to address the concerns of local authorities.
Dock workers fearing job cuts have opposed the further privatisation of both Piraeus and of Thessaloniki Port Authority , operator of the country's second biggest port which is also 74 percent government-owned.
Container port workers across the country walked out and demonstrated in central Athens on Monday, asking for both sales to be cancelled.
"It's a kind of policy that undermines the country's growth because it sells its advantage, Piraeus and Thessaloniki ports, to foreign state monopolies," the head of Greece's port workers union George Georgakopoulos told Greek television.
"The fire-sale of the port should stop."
The sale of a 51 percent stake in Piraeus could fetch about $200 million based on the company's market value of just under $390 million on Monday.
The port, a gateway to Asia, eastern Europe and northern Africa, handled 16.8 million passengers and 3.6 million 20-foot equivalent units (TEUs) of containers last year. Cosco has been operating one of the port's container terminals since 2008, the only terminal which remained opened on Monday.
Privatisations, a key element of Greece's bailouts since 2010, have produced revenue of only 3.5 billion euros so far. Athens concluded a 1.2 billion-euro airport leasing deal with Germany's Fraport earlier this month, hoping this would help it to meet its target for privatisation proceeds of 3 billion euros next year.
(Reporting by Angeliki Koutantou; Editing by Greg Mahlich and Jane Merriman)