The toll increased from 76 to 81 when a person succumbed to his injuries at a hospital while four other bodies were found around the region.
Late Tuesday, Fire Brigade Department spokesman Stavroula Mallire said the wildfires had injured 164 people, including at least 23 children, while more than 100 people were still missing.
Greek Prime Minister Alexis Tsipras has already declared a three-day national mourning period.
“The country is going through an unspeakable tragedy,” Prime Minister Alexis Tsipras said in a televised address on Tuesday.
“Today, Greece is mourning and we are declaring three days of national mourning in the memory of those who perished,” he added.
The nation is mourning the lives lost, with flags at parliament flying at half-mast.
Speaking to local TV channel SKAI, Rafina-Pikermi Mayor Evangelos Bournos said on Tuesday it is feared the death toll may reach 100.
Also, over 1,000 houses were destroyed, while hundreds of cars were made unusable due to the fire in Mati.
According to the Fire Department, 47 fires broke out in the country over the last 24 hours; 15 out of the total were around Athens.
The coastal region on the western side of Attica, Kineta -- around 54 kilometers (34 miles) west of Athens -- was evacuated when fires broke out Monday afternoon in a forest in Geraneia Mountains that surround the area.
The fire in Kineta region is yet to be brought under control.
Some casualties occurred when people were stuck in their homes or vehicles, or when they drowned in the sea while trying to escape the flames.
More than 700 people who escaped the fire and reached the shores were transported to safe areas by coast guard teams and private boats.
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