China and Greece have signed business deals worth about $5bn (£2.9bn) during Chinese Premier Li Keqiang's visit.
Deals signed covered areas including exports and shipbuilding. China also showed an interest in buying railways and building an airport in Crete.
China is eager to take a majority stake in the Piraeus port. A Chinese company already runs two piers at the port.
Greece is keen to attract foreign investment to reduce its national debt and high unemployment rate.
Mr Li has been in Greece as part of a tour of European countries. It is his first visit there since he took office in 2013.
"China attaches great importance to Greece's unique geographic advantage of being a gateway to Europe," the two countries said earlier in a joint statement.
Greek Prime Minister Antonis Samaras said China was interested in Greece's airports, and he hoped the country could "become a transit hub for air transport".
Mr Li described the port of Piraeus as "a pearl in the Mediterranean Sea" and said it could become "one of the most competitive ports of the world".
China's state-run shipping company, Cosco, won a 35-year lease to expand two main container terminals at the port in 2008.
It also wants to invest $310m (£180m) in expanding the port, in a deal that would require European Union approval.
The latest deals are a win-win for both countries - Greece desperately needs to raise funds and China wants a gateway to Europe at a price it likes, the BBC's Mark Lowen in Athens reports.
However, not all Greeks are delighted: the opposition says the government is selling the family silver on the cheap, our correspondent adds.