According to reports, traffic came to a standstill about 100 km north of Athens, just north of Lake Yliki.
A 14 km long jam formed, as thousands of Athenians were travelling north for the Christmas holidays.
Officials say that it could take hours to clear the highway from the snow. More than a dozen snowplowing vehicles are operating in this particular section of the road.
Heavy snow has caused problems in other parts of Greece, as well. Emergency services freed passengers of a bus that was stranded near Kalavryta, in the Peloponnese.
Traffic police is urging drivers to exercise extreme caution as night falls and ice forms on the roads.