Updated

Greece has formally signed an agreement to sell a 67 percent stake in operating Greece's biggest port to China's Cosco group, a significant step in the debt-crippled country's ambitious privatization drive.

Cosco's 368.5 million-euro ($420 million) offer was approved in January, in a process initially opposed by Greece's left-wing government.

Cosco, owned by the Chinese government, was the sole bidder for the stake in Piraeus Port Authority, a listed company which has a concession to operate the port until 2052.

Greece will retain a 7 percent stake and private investors will hold the remainder.

The deal still needs to be approved by Greece's competition commission and Parliament.

Piraeus is the main gateway to the Greek islands and in 2014 handled 16.8 million passengers.