There was no official indication how many people might be missing, and some people took to social media and Greek television stations with appeals for information on their loved ones.
The death toll is expected to increase as crews search more of areas affected by the fires.
More than 280 firefighters are still in the area north east of Athens, dousing the remaining flames to prevent flare-ups.
Another 200 firefighters are tackling a second forest fire west of Athens, where local authorities pre-emptively evacuated three nearby communities overnight, according to the fire department.
Fuelled by 50mph winds that frequently changed direction, the fires spread at speeds that surprised many, trapping hundreds on beaches and cutting off escape routes.
All the casualties appeared to be from the fire near Rafina, a popular seaside area that is a mix of permanent residences and holiday homes. The blaze broke out on Monday afternoon during a hot, dry spell but the cause was not immediately clear.
Aerial photos showed charred swathes of forest and homes.
Prime minister Alexis Tsipras declared three days of national mourning. Apart from the dead, who included children, hospitals treated 187 people, most for burns, with 10 listed in serious condition.
Twenty-six of the dead were found after dawn on Tuesday, huddled in a compound near the sea in the community of Mati, the worst-hit area near Rafina, about 30 miles west of Athens.
Red Cross rescuers said they appeared to be families or groups of friends because they were found hugging in groups of threes and fours.