Snowstorms have caused transport chaos around the Greek capital Athens, with one overnight traffic jam stretching for up to 15km (9 miles).
Ferry services were disrupted and there were power cuts in some parts of the capital and on the islands, prompting some schools to close.
Greeks have been warned to make only absolutely necessary journeys.
The sudden wintry weather struck late on Monday as many people were returning from a long weekend.
Ash Monday, the day Greek Orthodox Christians begin the religious season of Lent, is a public holiday in the country.
A national highway in Athens and roads in the city's northern suburbs were closed overnight, Reuters news agency reports.
Some roads in the Peloponnese, central Greece and the north of the country were also shut, according to the Greek news website Ekathimerini.
The snow that closed down the road at Malakasa was comparatively light and Transport Minister Dimitris Reppas accused the consortium that manages it, Nea Odos, of failing to do its job properly.
Nea Odos spokesperson Fotini Lambrou told Skai TV that 50 gritting machines had spread some 50 tonnes of salt on the road and that tailbacks had been caused by drivers reducing their speed or stopping to fit snow chains.
An area of low pressure situated across eastern parts of the Mediterranean is bringing in gale force winds with sustained speeds of 64km/h (40mph) and gusts of up to 128km/h (80mph).
Extensive warnings for coastal flooding have been issued for Tuesday, and the strong north-easterly winds will also significantly lower temperatures.
The cold weather is expected to last into Wednesday, with night-time temperatures in Athens dipping just below zero.