A tropical or subtropical system known as a “Medicane” has formed in the Mediterranean Sea bringing with it heavy rain and strong winds to parts of Greece and southern Italy.
There are fears the death toll will keep rising as home and businesses were destroyed by the torrential rain.
The industrial towns of Mandra, Nea Peramos and Megara near the capital Athens were the worst affected.
Many of the dead were elderly rescue crews found in their own homes.
A severe overnight storm turned roads into torrents of mud and debris, even vehicles were swept away smashing into buildings and fences.
A number of walls collapsed with the force of the mudslide filling streets and yards with rubble.
Parts of the major Athens – Corinth highway have been completely cut off due to the heavy rainfall.
Fire crews recovered the body of a man from the basement of flooded home and a woman was found dead in a local store in an area hit by severe flash flooding on the western outskirts of the Greek capital, bringing the death toll to 13 this evening.
Eleven of the fatalities — four women and seven men — were in the small town of Mandra, the area hardest hit by the flooding. The coast guard recovered the bodies of another two men from the sea, where they were believed to have been swept by floodwaters.
Several people were being treated in a hospital for various injuries, including hypothermia.
The fire department said it had received more than 600 calls for help pumping water out of buildings and rescuing people trapped in vehicles and homes.
It has appealed to the public to avoid the worst affected areas unless absolutely necessary.
More hazardous weather is predicted for across Greece later tonight and the next few days, including a storm warning for Athens.
The deaths near Athens come after a state of emergency was declared on the Aegean island of Symi after torrential rain flooded homes and power across the island was cut after the power station was flooded.