Three people became the first known fatalities on Tuesday of wildfires that have been raging on the Greek islands for a week, and Prime Minister Kyriakos Mitsotakis warned of tough days ahead as the blazes destroyed homes and forced tourist evacuations.

Two pilots were killed when their Canadair CL-215 plane fighting wildfires crashed on the island of Evia, east of Athens, the air force said. It gave their ages as 34 and 27.

TV footage showed the plane dropping water over a fire and then crashing into a hillside and bursting into flames.

State broadcaster ERT separately reported that the body of a 41-year-old stockbreeder who had been missing since Sunday was found burned in a shack in a hard-to-reach area on Evia.

Hundreds of firefighters, helped by forces from Turkey and Slovakia, have been battling blazes that have raged on the islands of Rhodes, Corfu and Evia since Wednesday and resurged in hot, windy conditions, while emergency planes have been flying out tourists.

Mitsotakis told ministers on Tuesday that the next days would be difficult, with conditions possibly improving after Thursday.

"All of us are standing guard," he said. "In the face of what the entire planet is facing, especially the Mediterranean which is a climate change hot-spot, there is no magical defence mechanism."

The high temperatures in Greece are set to rise through Wednesday to exceed 44 Celsius (111 Fahrenheit) in some areas.

An assessment by scientists published on Tuesday said human-induced climate change had played an "absolutely overwhelming" role in extreme heatwaves that have swept across North America, southern Europe and China this month.

'Unprecedented ordeal'

Lefteris Laoudikos, whose family owns a small hotel in the Rhodes seaside resort village of Kiotari, one of the epicentres of the fire over the weekend, said its 200 guests - mainly from Germany, Britain and Poland - evacuated in rental cars.

He said his father, cousin and two others were trying to douse the flames using a nearby water tank.

"On Saturday when I saw the wind and that there were no planes, I told everyone 'we're going to burn today,'" he said.

"My father saved the hotel. I called him, and he didn't want to leave. He told me 'if I leave there will be no hotel'."

John Hatzis, who owns three unaffected hotels in northern Rhodes, said the island needed to welcome back tourists.

"After the superhuman efforts to contain the fire we need superhuman efforts to restart tourism now," he said.

Rhodes, one of Greece's biggest islands, is among its top summer destinations, attracting about 1.5 million foreign tourists in the summer months.

About 20,000 people had to leave homes and hotels in Rhodes over the weekend as the inferno spread and reached coastal resorts on the verdant island's southeast, after charring land, killing animals and damaging buildings.

After a blaze in the seaside town of Mati, east of Athens, in 2018 killed 104 people, Greece has taken a more proactive approach towards evacuations. But critics say it has not improved its ability to put out fires that are common in summer, though more intense in this year's heatwave.

The mayor of Rhodes said on Facebook the island was facing an unprecedented ordeal. A prosecutor had launched an investigation into the causes of the fires and the preparedness and response of authorities, ERT reported. It said about 10% of the island's land area had burned.

Around 3,000 holidaymakers had returned home by plane by Tuesday and tour operators cancelled upcoming trips. TUI dropped flights to Rhodes through Friday.

Tourism accounts for 18% of Greece's economic output and one in five jobs. On Rhodes and many other Greek islands, reliance on tourism is even greater.