Greece's parliament was closed on Monday, while a number of schools in the country also reverted to online classes.
Heavy snowfall has caused major travel disruption to international airports in Greece and Turkey.
Istanbul International Airport -- Europe's busiest airport in 2021 -- said it had suspended all operations on Monday until midnight.
In a statement on Twitter, the general management of civil airports in Turkey said that "exceptional conditions" and strong winds had reduced visibility on the runways.
Turkish Airlines also decided to cancel all its flights to and from Istanbul Airport until 04:00 on Tuesday for "the safety of its passengers".
A spokesperson said one of the airline's cargo terminals had collapsed under the weight of snow at the main international airport. No casualties have been reported.
The Sabiha Gökçen Airport in Istanbul was still operating normally on Monday despite several reported delays.
Interior Minister Suleyman Soylu said the snowfall in and around Istanbul would continue until Thursday and urged people not to venture out in private cars unless necessary.
Snow has also covered much of Greece as far south as the island of Crete, as a result of a cold snap with temperatures as low as -14 degrees Celsius.
Hundreds of motorists were trapped for several hours on the Athens ring road while huge traffic jams disrupted traffic on other roads. The army was sent out overnight to deliver food and water to those trapped and to help free as many as possible.
Officials said the Greek Prime Minister Kyriakos Mitsotakis had contacted the highway’s administration and asked for each trapped driver to receive €2,000 euros in compensation.
Elsewhere, several people were injured when a rail engine collided with a passenger train that it had been sent to rescue from the snow near the town of Livadia.
A number of Greek schools and the country's parliament were closed on Monday, while the metro line to Athens' main airport was also disrupted.
Meteorologists have told national media that the Greek capital has not experienced such weather conditions since 1968.
Snow even fell on several Greek islands in the Aegean Sea, isolating some mountain villages on Andros, Naxos, and Tinos and covering the beaches of Mykonos.
Heavy snowfall also occurred on the island of Evia, north of Athens, which was ravaged by fires last summer. Municipalities there have redoubled their efforts to keep the main roads open, while many villages suffered power cuts on Monday.
With the snowfall expected to continue on Tuesday, Greek authorities have announced the "suspension" of private and public services for Tuesday, with the exception of police, fire brigades, and hospitals.
Meanwhile, in neighbouring Albania, all schools will be closed for three days due to the cold weather.