A coastguard spokeswoman said a man and woman had died at the Sarakiniko beach on the tourist island of Milos in the Cyclades, as firefighters battled blazes near Athens and the island of Cephalonia.

"The man and woman were found unconscious in the sea and were taken to the local health centre," the spokeswoman 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 the Sea of Crete.

Over 200 firefighters backed by three aircraft and five helicopters were battling a fire in Keratea, east of Athens, Costas Tsigkas, head of the association of Greek firefighter officers, told ERT state television.

"It's a difficult fire...(owing) to wind gusts," he said, adding that a number of local communities had been evacuated.

The Cephalonia fire was earlier placed under control, local officials said.

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 had shut down the National Garden on Thursday 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.