Five people, a hotel owner and staff among them, were found dead in Areopolis, a village on the Mani peninsular in the Pelopennese.
Two other bodies have not yet been identified. The sixth person, a firefighter, died from a heart attack at the scene.
Local authorities have declared a state of emergency in the southern regions of Messenia and Laconia. Major fires are now also burning in the mountains of Parnon and Taygete. Residents have been evacuated.
Blazes are also tearing through Elefsina, central Greece, where oil tankers from the nearby refinery are kept.
The northern outskirts of Athens have been affected by smoke from fires in the region of Penteli mountain.
Firefighters said strong winds up to 55-63 miles per hour (88-102 kilometers per hour) have hindered firefighting efforts in the area.
Earlier Greece announced that up to 40,000 hectares of forest had burned down in the country so far this summer. In the provinces of Attica in southern Greece and Boeotia in the east, more than a sixth of the woodland has been destroyed.
