ATHENS (Reuters) - Piraeus Port <OLPr.AT> shareholders approved a new concession agreement with Chinese shipping giant COSCO <601919.SS> on Friday, bringing Greece a step closer to concluding the sale of a majority stake in the port.

Greece agreed in April to sell a 67 percent stake in the port to COSCO for 368.5 million euros. With the concession agreement approved, the deal now needs the green light from parliament and the competition watchdog to go through.

Privatizations have been significant elements in Greece's succession of bailouts since 2010 but have reaped poor revenues due to political resistance, union protests and bureaucracy.

Under its third international bailout, Athens also plans to sell a majority stake in its second largest port in the northern Greek city of Thessaloniki <OLTr.AT> later this year.

Last week, Piraeus Port shareholders met at an Athens hotel to clear the concession agreement, which specifies how COSCO will operate the port, and the removal of workers representatives from the board, but the meeting was interrupted due to protests by striking port workers.

They have been on 48-hour rolling strikes since late May, opposing the sales of the ports and demanding their labor status be protected under the privatization deals, including the concession agreement with COSCO.

On Friday, they gathered again outside the Athens stock exchange where Piraeus shareholders met under the presence of about 300 police officers.

The port workers have refused to return to work until they get written assurances from the government that their rights will be secure.

"We don't have any basic assurances for the future of the workers both at Piraeus and Thessaloniki ports," the head of port workers union George Georgakopoulos told Reuters. "We will continue our fight and we will scale it up until the end."

Dozens of state workers blocked the entrance to offices of Greece's privatization agency in Athens earlier on Friday to protest against the port sell-offs.

The port strike has disrupted cargo operations and services provided to cruise ships. Cruise operators have warned they will shun Piraeus in favor of other ports if the action continues.

(Reporting by Angeliki Koutantou; editing by David Clarke)