ATHENS (Reuters) - Greek Prime Minister Kyriakos Mitsotakis said on Monday he had approved a supplemental budget of 500 million euros ($587 million) to fund relief and compensation for people who have lost homes and property in wildfires that have hit the country.

       "The extent of the destruction blackens our hearts, I apologise for the losses," Mitsotakis said in a televised address, promising his government would stand by all those hurt by the blazes.

       Firefighters on the ground and from the air were still battling to halt wildfires on the island of Evia, Greece's second largest near Athens, as they threatened to engulf the town of Istiaia in the north of the island.

       Strong winds fuelled flare-ups on the island after the fires appeared to ease earlier on Monday. Water-bombing aircraft struggled to operate because of the large plumes of smoke blanketing the area, authorities said.

       "Those who lost homes and property will be compensated. The burned areas will be reforested," Mitsotakis pledged.

       The government's relief measures will be detailed after a cabinet meeting on Tuesday.

       Mitsotakis said government services had to deal with 586 wildfires "in all corners of Greece" amid a heatwave. He thanked countries that sent assistance and the many volunteers who helped firefighting efforts.

       He said possible failings would be investigated. Angry Greeks are criticising the government's response to the devastation.

       "The climate crisis is knocking on the door of the entire planet," he said.

       ($1 = 0.8516 euros)

       (Reporting by George Georgiopoulos; Editing by Mark Potter)