The incident, involving a man and a woman, happened at Sarakiniko beach on the tourist island of Milos in the Cyclades, a coastguard spokeswoman told AFP.

"The man and woman were found unconscious in the sea and were taken to the local health centre," she said.

"They were Vietnamese tourists on a cruise ship group. The woman fell in the water and the man apparently tried to save her," she said.

The civil protection ministry said wind gusts would reach 88 kilometres (54 miles) an hour, especially in the southern Aegean and Sea of Crete.

National weather service EMY said the phenomenon would weaken after midnight.

The coastguard said most ferries were unable to depart on schedule from Piraeus and other Athens ports, especially to the Cyclades or Dodecanese islands.

Several planned ferries were cancelled while others were postponed.

Maritime connections with the Saronic islands near Athens including Aegina, Hydra, Poros, and Spetses and the Ionian Sea are unaffected, it said.

The Athens National Observatory in a statement also warned there was a "very high potential for wind-driven forest fires", particularly in the east and south of the country.

The mayor of Athens on Thursday shut down the National Garden after a tree fell in one of the capital's busiest high streets, narrowly missing shoppers.

Strong winds are common in Greece at this time of year.