In certain regions of the Mediterranean nation, highs of 43C (109F) were predicted for Wednesday and Thursday.
The high temperatures are caused by southerly winds carrying hot air and dust from North Africa, according to meteorologists.
Due to the potentially fatal temperatures on Wednesday, the Acropolis, an archaeological monument that welcomed four million visitors last year, was closed from 9 a.m. to 2 p.m. (GMT).
In addition, primary schools and nurseries in the southern regions of the country were closed until Friday, when colder weather is predicted. Red Cross medics were also observed giving water bottles to visitors.
In addition, seven air-conditioned areas will be made available to the public, and city officials said that waste collection will be suspended for a few hours.
The city will also deploy drones equipped with infrared cameras to plan a public health response.
According to the Greek fire department, dozens of firemen were battling a fire that started at a cookware business near Athens on Wednesday.
42 firefighters and 14 fire engines were dispatched to the scene in the Kifisa suburb in the north.
In order to protect themselves, locals were advised to stay indoors. It took some time to determine what started the fire.
