Wildfires raging through seaside resorts near the Greek capital torched homes, cars and forests, killing at least 74 people, authorities said on Tuesday (Wednesday NZT).

Twenty-six of the dead were groups of families or friends found huddled together, some of them clasp in hugs. Others swam out to sea to escape the inferno and some never came back.

Greece endures wildfires every year but the fires that broke out on Monday (Tuesday NZT) were the deadliest to hit the country in decades. Fueled by gale-force winds, they trapped thousands of people on beaches, roads and in homes.

At least 74 people are confirmed to have died, with many more injured, as wildfires rage near Athens.

Prime Minister Alexis Tsipras declared three days of national mourning for those killed as officials feared the death toll could rise even further, as there was no definitive count of how many people were missing.

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The raging wildfires on the outskirts of the Greek capital Athens have torched homes, forest and cars.

Coast guard boats patrolled the shores near fire-hit areas on Tuesday (Wednesday NZT) after over 700 people trapped by quick-moving fires had to be rescued from beaches or the sea, where six of the dead were found.

While Greek authorities urged the public to contact them if they were looking for loved ones, many people took to social media, posting pictures of those they were looking for and their last known location before the fires hit.

Fire service spokeswoman Stavroula Malliri announced Tuesday afternoon (Wednesday NZT) that the death toll had jumped from 50 to 74. In addition, 164 adults and 23 children were still being treated in hospitals for injuries, mainly burns. Of the adults, 71 remained hospitalised , 10 of them in serious condition, while 11 of the children also remained hospitalised.

THANASSIS STAVRAKIS/AP Authorities have declared a state of emergency in the eastern and western parts of the greater Athens area as fires fanned by gale-force winds raged through pine forests and seaside settlements on either side of the Greek capital.

Twenty-six of the dead were found at first light on Tuesday huddled together in one compound near the sea in the community of Mati, near the port of Rafina. Red Cross rescuers who found them said they appeared to be families or groups of friends, as they were found hugging in groups of threes and fours.

"Instinctively, seeing the end nearing, they embraced," the Red Cross said .

Although the fires had largely abated by Tuesday afternoon (Wednesday NZT), they were far from out. Firefighters, aided by water-dropping aircraft from the sky, were tackling the remaining areas in the two main blazes near the capital: one northeast of Athens near Rafina, where most of the casualties appeared to have occurred.

THANASSIS STAVRAKIS/AP Buildings burn in the town of Mati. A state of emergency has been declared in the eastern and western parts of the greater Athens area as fires fanned by gale-force winds raged through pine forests and seaside settlements.

In the other major fire, about 50km west of Athens, some flare-ups were reported on Tuesday afternoon (Wednesday NZT). Fires continued to burn in other parts of the country too, with one on the island of Crete the most severe.

With the flames whipped up by gale-force winds that frequently changed direction, many tourists and residents fled toward the coastline. Some swam out to sea, braving rough water and strong currents to escape the ferocious flames and choking smoke.

The speed of the fire's advance took many by surprise.

Forest fires erupt in several places around the Greek capital, destroying homes and disrupting transport links.

"It happened very fast. The fire was in the distance, then sparks from the fire reached us. Then the fire was all around us," resident Nikos Stavrinidis, who had gone with his wife to fix up his summer home for a visit by his daughter, told The Associated Press.

Stavrinidis, his wife and four friends swam out into the sea to escape the smoke, but they quickly became disoriented, losing sight of the shore and being swept out further by the wind and currents.

Two of the group didn't survive.

THANASSIS STAVRAKIS/AP A firefighter sprays water on the fire. Hundreds of emergency personnel have been called in to fight the blazes.

"It is terrible to see the person next to you drowning and not being able to help him," Stavrinidis said, his voice breaking. The remaining survivors were picked up by a fishing boat with an Egyptian crew who jumped into the water to rescue them.

A flotilla of coast guard and private boats evacuated more than 700 people from threatened beaches overnight, authorities said. Defense Minister Panos Kammenos said 88 people had been picked up from the sea by a military vessel.

"Everything happened in seconds," said Andreaas Passios, who lives next to the compound in Mati where the 26 bodies were found. "I grabbed a beach towel. It saved my life. I soaked it, grabbed my wife and we ran to the sea."

AP People stand in the sea near cars parked on the beach as the fire rages near the seaside town of Mati.

Passios said he and his wife stayed by the sea for two hours.

"It was unbelievable. Gas canisters were exploding. Burning pine cones were flying everywhere," he said.

When the flames died down, Spyros Hadjiandreou came searching for loved ones.

AP People cover their faces from the smoke that fills the sky near Kineta, west of the capital Athens.

"My niece and cousin were staying here on holiday. I don't know if they made it out," he said. "I don't know if they are OK. I haven't heard from them."

Fanned by gale-force winds, the flames spread rapidly into seaside towns, moving too fast for many who were in their cars or homes to flee, Malliri said.

"The police tried to direct us away from the fire, but we couldn't escape it," said Aleka Papariga, a former Greek Communist Party leader who lives near Rafina. "We got stuck in traffic and the flames were on top of us. We managed to find a small gap and we made it out."

AP Scores of people have been injured by the wildfires, with dozens of homes destroyed.

Evangelos Bournous, the mayor of Rafina, blamed the winds.

"We were unlucky," he said. "The wind changed and it came at us with such force that it razed the coastal area in minutes."

Rafina's dock became a makeshift hospital during the night as paramedics checked survivors, some clad in only their bathing suits, who emerged from coast guard vessels and private boats.

In all, 47 brush and forest fires broke out across Greece on Monday and early Tuesday (Tuesday NZT), with most of them quickly extinguished, the fire department said.

Greece sought international help through the European Union. Spain was sending two firefighting aircraft while Cyprus was sending in 60 firefighters. Israel, Turkey and Bulgaria also offered assistance.

Heavy rain was forecast across southern Greece on Wednesday, with hopes they could help in the firefighting effort.

Forest fires are common in Greece during its hot, dry summers, and temperatures recently reached up to 40deg C.

In 2007, more than 60 people were killed when huge fires swept across the southern Peloponnese region.

NZ officials are in contact with local authorities, but say there are no indications any New Zealanders have been caught up in the fires. There are currently 162 New Zealanders registered on SafeTravel as being in Greece.