A Greek and a Dane have been killed in a mid-air helicopter crash while fighting wildfires, with a British pilot among the survivors.
Emergency services rushed to the scene after the aircraft collided in the Psatha region of Attica, 42 miles west of Athens.
The helicopters, manufactured by US company Bell, were each carrying two passengers and had taken off from the Elefsina military airport.
Striking footage shows one of the aircraft slowly approaching the other - before their rotors clash and the helicopter erupts into a fireball and plummets into a ravine.
The crew members were taken to the 251st Air Force General Hospital after the crash, according to local media.
Two of the four involved were found unconscious while the other two - a British pilot and a Greek fire service liaison officer - are believed to have sustained light injuries.
Foreign firefighting and helicopter crews are often deployed in Greece to help tackle wildfires during the country's hot, dry summers
'The pilots... were taken unconscious to hospital, where their death was confirmed,' the fire department's director of communications Vassilis Vathrakogiannis said.
The helicopters had been leased from Australia's McDermott Aviation, part of a fleet of 15.
Two helicopters have crashed into each other while fighting wildfires in Greece. They collided in the Psatha region of Attica, west of Athens
Striking footage shows one of the aircraft slowly approaching the other - before their propellers clash and the helicopter erupts into a fireball and plummets to the ground
The aircraft were both carrying two passengers and had taken off from the Elefsina military airport
Wreckage of the helicopter strewn across a road near Psatha on Sunday evening
The company has said it has supported operations in Greece for the past seven years.
The fire department grounded all Bell helicopters in the area pending an investigation, state TV ERT said.
Greek Prime Minister Kyriakos Mitsotakis expressed 'sorrow for the tragic accident' and extended condolences to the families of the firefighters killed in the crash.
'The loss of the Greek coordinator and the Danish pilot at the time they were attempting the major fire in Porto Gremeno fills us all with grief,' Mr Mitsotakis said in a statement.
The accident raised the death toll from this week's Greek fires to five, after three firefighters died in Crete and the Peloponnese.
Hundreds of firefighters were today battling wind-fuelled fires near Porto Germeno - a short distance north from Psatha - on the Gulf of Corinth, north-west of the capital.
Authorities said strong winds made the fire spread more quickly and made it unpredictable for firefighters.
'The situation is extremely hard, especially today. We have really strong winds, gusts exceeding 73 kph (45 mph). The direction of the fire can't be determined easily,' doctor and firefighter Giorgos Doulas said.
The fire department's deputy spokesman Yiannis Artopios told state TV ERT that the wind was so strong that firefighters on the scene 'couldn't even open their vehicle doors'.
Greece's prime minister issued a warning about firefighting aircraft hours before the crash - saying they could not 'operate safely' in strong winds.
Kyriakos Mitsotakis made the comment in a Facebook post earlier today as he said despite the government's 'investment' of resources, there were 'times when the nature and intensity of weather phenomena exceed all human planning and operational capabilities'.
Mr Mitsotakis added: 'When winds blow with such intensity, even the dozens of aerial assets at our disposal cannot operate safely.
'On several occasions in recent days, it was impossible to either draw water or drop it, as extreme turbulence made flights impossible, with the result that the burden of the fight fell almost exclusively on the people on the front lines.'
Nearly 500 Greek firefighters have been deployed to the region, assisted by emergency crew from France and Romania.
It comes as over 100 homes have been destroyed amid gale-force winds that have fueled flames in the area.
An ambulance is seen heading to the area where two firefighting helicopters crashed in Psatha, during a fire in the wider region of Megara
Firefighters are seen battling bright orange flames caused by a wildfire near the village Agia Paraskevi, Greece
Trees burn during a wildfire near the village Agia Paraskevi. The region north of Athens has been badly affected
A Greek firefighter tries to extinguish a wildfire in the area of Porto Germeno, some 45 miles northwest of Athens
A firefighter stands as flames rise during a wildfire near Porto Germeno, northwest of Athens in Greece
A firefighting helicopter drops water over a wildfire in the area of Porto Germeno, just 45 miles off Athens
Authorities said strong winds made the fire spread more quickly and made it unpredictable. Emergency crew are seen tackling the blaze here
A military firing range is among the sites affected.
More than 200 people from the town of Agios Vasileios had to be evacuated by sea this week.
Around 500 people, mostly tourists, were left stranded after a fire broke out near the village in Viotia, central Greece, on Friday morning and rapidly spread in strong winds, local media reported.
Footage showed residents and holidaymakers boarding boats as volunteers and rescue teams worked to remove those from the town.
Other videos showed how smoke swirled around in the air as people flocked to board vessels.
People there had previously been told by authorities to move inland before the fire reached the outskirts of the town.
Wildfires have also affected the Peloponnese peninsula and the islands of Crete, Paros and Lesvos - popular tourist destinations.
While the Foreign Office does not advise against travelling to Greece it said 'there is a high risk of wildfires'.
It added that travellers should ensure that their 'mobile phone is registered to receive emergency alerts to be warned of wildfires'.
Europe has been ravaged by wildfires this summer after successive record-breaking heatwaves, leaving vast stretches of drought-parched vegetation primed to burn, and forcing hundreds of thousands of people to flee their homes.
In Italy, authorities put nearly all of its major cities on the highest 'red' alert for high temperatures as a new heatwave threatened to grip the country.
Some 19 cities including Rome, Milan, Venice and Naples will now be on the alert as temperatures are set to hit the mid 30s C next week.
Successive heatwaves have created favourable conditions for wildfires across Europe and Britain.
A wildfire in Suffolk this week burnt 371 acres - equivalent to 210 football pitches and took hold near Britain's biggest nuclear power station Sizewell B.
High temperatures can also be unsafe and could be dangerous even to healthy and active people, not just the elderly, the very young or people with chronic illness.
Austria recorded 395 heat-related deaths in June. Earlier this week, 2,877 people died from heat in Britain so far this year, while France reported 5,664 excess deaths in the country between June 17 and July 2.
Germany's health authority recorded around 9,800 deaths this year linked to high temperatures.
