Greece on Saturday reopened six of its main ports to cruise ships for the first time in the coronavirus-shortened tourism season, but no ships are expected before three weeks.

In a letter to the Cruise Lines International Association and three major cruise operators early this week, Tourism Minister Harry Theoharis said the ports of Piraeus in Athens, Rhodes, Iraklio, Volos, Corfu and Katakolo would accept passengers, state agency ANA reported.

After docking at one of the six ports, cruise ships will be able to travel elsewhere in Greece, depending on local coronavirus conditions. But shipping minister Giannis Plakiotakis said on Thursday that cruises would only restart after August 20.

He said foreign cruise lines had expressed their interest in operating in Greek waters but that "cruises are an international operation and face serious problems because of the coronavirus". With a quarter of the economy dependent on tourism, Greece has sought to capitalise on its relatively low infection rate to bring in visitors.

So far officials have announced nearly 4,500 infections and 206 deaths. Last month, Greece began to reopen its land borders to select countries, before allowing mostly European flights to all its airports on July 1.

Since then, there have been over 340 confirmed infections among nearly 1.3 million incoming travellers, the civil protection agency said Tuesday. But demand is below expectations: The occupancy rate of Greek hotels is only a fifth, according to the Hellenic Chamber of Hotels, and local cruise operators do not expect bookings before September.