Survivors of the major forest fires that ravaged a seaside area of Greece say the flames came upon them in "the blink of an eye", forcing them to flee into the sea or drive through the smoke to escape.

Key points: At least 80 dead with toll expected to climb

At least 80 dead with toll expected to climb Residents recall swimming in the ocean as the fire passed

Residents recall swimming in the ocean as the fire passed Three days of mourning declared

The fires have killed at least 80 people and injured 187, officials said, and Greek Prime Minister Alexis Tsipras has declared three days of national mourning for the dead.

The number of victims appeared set to climb, with crews checking charred homes and vehicles and the coast guard scouring beaches and deeper waters.

There was no definitive count of the missing.

Sorry, this video has expired Bushfires tore through coastal towns not far from Athens (Photo: AP)

Fuelled by 80 kilometre per hour winds, the fires left scores of gutted cars lining streets in the coastal town of Mati, east of Athens, melted by the intensity of the heat.

Bodies lay on roadsides, and in one area, a group of 26 people were found dead — some locked in an embrace as the flames closed in.

The group, which included children, was found near the top of a cliff overlooking a beach.

They had ended up there after apparently searching for an escape route.

"Instinctively, seeing the end nearing, they embraced," the head of Greece's Red Cross, Nikos Economopoulos, told Skai TV.

People gather at the beach seeking respite from the wildfires in Mati. ( Nikos Kalogerikos via Reuters )

The lucky ones were able to leap off the cliffs to survive, or rush into the sea from the beach.

"We went into the sea because the flames were chasing us all the way to the water," said Kostas Laganos, a middle-aged survivor.

"It burned our backs and we dived into the water."

Nikos Stavrinidis had gone to his summer home in the Mati area with his wife to prepare it for his student daughter, who was coming to stay.

Sorry, this video has expired A man grieves over a destroyed car where he last saw his wife.

Before he knew it, the fire surrounded him.

"It happened very fast. The fire was in the distance, then sparks from the fire reached us. Then the fire was all around us," Mr Stavrinidis said.

"We ran to the sea. We had to swim out because of the smoke, but we couldn't see where anything was."

Flames forced many people to flee into the water. ( AP: Thanassis Stavrakis )

There were six people in his group: Mr Stavrinidis, his wife and some of her friends.

They swam further out to escape the smoke, but as they did so, they began to be carried away by the wind and the current.

They lost sight of the shore and became disoriented.

"We couldn't see anything," he said.

A woman searches for her dog after the fires at the village of Mati, near Athens. ( Reuters: Costas Baltas )

Gale-force winds fanning the flames in the area also hampered firefighting efforts and whipped up the seas.

"We didn't all make it," Mr Stavrinidis said. One of the women in his group and one woman's son drowned.

"What upsets me and what I will carry in my heart is that it is terrible to see the person next to you drowning and not be able to help him. You can't. That's the only tragic thing," he said.

Nikos Stavrinidis fled from the Greek forest fire into the sea with his friends, but said not all of them survived. ( AP )

Mr Stavrinidis said he believed they were in the water for about two hours before being picked up by a fishing boat with an Egyptian crew.

"I'm grateful to all of them," he said.

"They jumped into the sea with their clothes still on. They made us tea and kept us warm. They were great."

People survey the destruction in Mati east of Athens. ( AP: Thanassis Stavrakis )

Andreaas Passios said "everything happened in seconds".

"I grabbed a beach towel. It saved my life. I soaked it, grabbed my wife and we ran to the sea," Mr Passios said.

Mr 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."

Sorry, this video has expired Two major forest fires are burning out of control on either side of Greece's capital.

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

"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."

Giannis Labropoulis from the city Patras, west of Athens, was driving along the highway when flames seemed to come out of nowhere.

He told the ABC's PM he knew there was a fire, but could not have imagined how fast it would appear.

"We were driving through the flames all of a sudden in the blink of any eye, to be honest," he said.

"We just saw the road going into smoke, and then all of a sudden the flames were on the left-hand side of the car.

"We were so kind of shocked, because although we were in an air-conditioned car, we felt the heat coming in.

"All the houses that were on the hill beside the highway, they were completely burnt out."

A fire truck is engulfed in a pall of orange smoke on a road near Kineta. ( AP: Thanassis Stavrakis )

Mr Labropoulis said the flames came within two to three metres of his car.

"We were able to drive just I think by luck, to be honest, because the things were going on so fast, the flames expanded so fast that we could not even imagine that in three seconds this thing could happen," he said.

"The problem was that as we were driving through with all these small branches from the trees flying around, we could hear the car going, 'tak-tak-tak'.

"It felt like somebody was kind of shooting at you."

Water-dropping planes and helicopters are battling a blaze in the Geraneia mountains between Athens and Corinth. ( AP: Theodora Tongas )

ABC/wires