Greek authorities declared today and tomorrow as public holidays as heavy snowfall clogged roads and stranded thousands of people.

In Athens, hundreds were evacuated from a motorway overnight and took shelter at the city's airport after yesterday's severe snowstorm.

The decision to announce two public holidays means shutting schools, public offices and private businesses except pharmacies, supermarkets and petrol stations.

This morning, dozens of cars were still covered in snow as ploughs tried to clear roads and anger grew among people trapped in freezing temperatures for hours.

"The situation is hopeless," said Spiros Kandaras, who spent 24 hours in his car. "They should be ashamed of this mess."

Cars abandoned in the snow at Athens' main ring road earlier today

Heavy snow is rare in Athens but the city has now been hit by extreme weather for a second consecutive winter.

More than 3,500 people had been evacuated by early today, some abandoning their cars on foot, but around 1,200 cars remained stuck on the Attiki Odos, the capital's main ring-road.

As temperatures fell overnight, soldiers shovelled snow and handed out food, water and blankets to drivers, some of whom were stranded in their cars for more than 10 hours.

Parts of Athens were hit by power cuts for several hours and the grid operator said crews were working to restore electricity.

Snow storm blanketed Athens in white

Some Istanbul Airport flights resumed today after nearly 24 hours of cancellations.

The Turkish airport - which is among the world's biggest - has been under a thick blanket of snow with runways and planes covered.

The snowfall began late last week and picked up over the past days in the city of 16 million people, delaying buses and ferries and prompting a ban on driving private vehicles.

"We have been here for more than 24 hours already," said Selim Kilik, who planned to fly to Paris this week. He complained about a lack of staff and information.

An airport spokesperson said limited flights began around 10am today after a 22-hour delay, and that scheduled flights would resume around midnight.

Turkish Airlines earlier said it had halted all flights until 9pm.

Storms swept through Greece and across Turkey, as well as into Syria, where snow has disrupted aid deliveries to displaced families living in tented camps.

In Turkey, snow carpeted the beaches of the southern resort city of Antalya for the first time in 29 years. In a rare sight, Greece's southern Aegean islands, including Mykonos, also turned white.

Stranded passengers wait at Istanbul airport

A video posted on social media showed a man skiing through Istanbul's streets, with people waving as he passed.

Governor Ali Yerlikaya took the rare step of banning private cars for several hours while public workers were given leave through tomorrow to keep commutes to a minimum.

Other footage showed trucks and cars stranded along highways in and around Istanbul.

People walk through snow in front of the Blue Mosque in Istanbul, Turkey

Passage across the Bosphorus Strait reopened today, while people were evacuated from stranded vehicles, said Transport Minister Adil Karaismailoglu.

Across the country, about 4,600 people were left stranded onroads and elsewhere, and thousands had been placed in temporary housing, the Disaster and Emergency Authority said.