Hundreds of firefighters have battled a wildfire that raged for a second day in mountains near Athens, burning homes and cars and forcing the evacuation of at least nine settlements and a hospital.

Gale-force winds and thick smoke in the Penteli region just north of Athens hindered fire-fighting efforts from the air and on the ground, authorities said.

The wildfire broke out around 2:30pm on Tuesday, local time, 27 kilometres north of the capital and was still burning on several fronts nearly a day later.

Penteli had previously suffered a wildfire in July 2018 and huge wildfires in 1995 and 1998 had burned more than 13,000 hectares.

As they battled the blazes, firefighters recovered the body of an 84-year old man who died from shotgun injuries, police said.

A fire brigade spokesman said the injuries appeared to be self-inflicted but the incident was still under investigation.

Authorities said ambulances took other three people to hospital with respiratory problems and slight burns.

About 485 firefighters and 120 fire engines were deployed to contain the blaze. Nine aircraft and 10 helicopters were dumping water on the flames on Wednesday.

"There are a number of destroyed homes and businesses. We will have a clearer count [on Thursday]," Pallini's Mayor, Thanasis Zoutsos, told state ERT TV.

In a televised statement, fire department spokesperson Yiannis Artopios talked of a "difficult night", as wind speeds exceeded 80kph and constantly changed direction, hindering efforts to tame the blaze.

Authorities ordered the evacuation of nine districts, including the Athens suburbs of Pallini and Gerakas.

One hospital and the National Observatory of Athens were also evacuated.

Last year, wildfires ravaged about 121,000 hectares of forest and bushland in different parts of Greece as the country experienced its worst heatwave in 30 years.

Meanwhile, in Italy, fire brigades in Tuscany battled a wildfire that forced hundreds to evacuate and caused gas tanks to explode, as smoke from a blaze in north-east Italy forced shipbuilder Fincantieri to shut down a 3,000-staff plant.

Nine cities were on the country's highest heatwave alert — which warns of serious health risks linked to the weather — up from five on Tuesday.

The number of cities with such a warning will rise to 14 on Thursday, including Rome, Milan and Florence.

Temperatures are expected to hit 40C across a wide area of the north and centre of Italy this week, as well as in the southern Puglia region, and the islands of Sardinia and Sicily.

The Tuscany blaze forced around 500 people to evacuate as flames raged through the night, reaching some villages and causing liquefied gas tanks to explode, the region's governor, Eugenio Giani, said.

In the north-eastern Friuli Venezia Giulia region, residents were urged to stay indoors because of heavy smoke from a wildfire that started on Tuesday in the Carso area bordering Croatia and Slovenia.

That fire prompted state-owned shipbuilder Fincantieri to close down its plant in the port city of Monfalcone.

Reuters