Heavy snowfall has left at least 150 villages cut off in Greece and severely disrupted flights to and from Athens.
Athens' streets looked virtually deserted on Monday
Many of the affected villages faced power outages, the Greek civil protection authority said.
Dozens of international and domestic flights to and from Athens' airport were cancelled, as up to 15cm (six inches) of snow blanketed the capital.
Schools in the city have been closed, and the authorities are urging people to stay indoors.
The worst affected were villages in the southern Peloponnese peninsula and also on the islands of Crete and Evira, officials said.
The country's civil defence authorities were on alert, and problems with power and water supply were reported across the country.
In parts of northern Greece, temperatures plunged to minus 11C (12F).
Up to 15cm of snow blanketed Athens
The streets of Athens - normally a bustling metropolis - looked almost deserted on Monday as many residents decided to stay indoors.
"I don't remember any such conditions in Athens before," public works ministry official Dimitris Katsigiannis told state NET television.
"Our concern was to keep road arteries open, and our engineers have worked around the clock for 48 hours," Mr Katsigiannis said.
Greek meteorologists said they expected weather conditions to improve later on Monday.