Wildfires sweeping through a Greek resort town have killed at least 74 people, officials say, including families with children found clasped in a last embrace as they tried to flee the flames.

Key points: At least 187 people, including 23 children, have been injured in the fires

At least 187 people, including 23 children, have been injured in the fires Reports a six-month-old baby died of smoke inhalation

Reports a six-month-old baby died of smoke inhalation Greece has called for assistance from neighbouring countries and the EU

At least 187 people, including 23 children, have been injured. The number of missing persons was still unclear.

The number outpaces the death toll of 2007, one of the worst on record, where about 70 individuals died from fires in the southern Peloponnese region.

Emergency crews found one group of 26 victims, some of them children, lying close together in a field just 30 metres from the sea near Mati in eastern Greece.

Nikos Economopoulos, head of Greece's Red Cross, told Skai TV they had tried to find an escape route "but unfortunately these people and their kids didn't make it in time".

"Instinctively, seeing the end nearing, they embraced," he said.

Merchant Marine deputy minister Nektarios Santorinios, whose ministry is in charge of the coast guard, said more than 700 people had been evacuated by sea by the coast guard.

The coast guard earlier said the bodies of three women and a child were found in the sea.

In total at least 74 people died, authorities said.

Greek Prime Minister Alexis Tsipras has declared three days of national mourning for the dozens of people killed.

"Today Greece is mourning, and in memory of those who were lost, we are declaring a three-day period of mourning," he said.

"But we mustn't let mourning overwhelm us, because these hours are hours of battle, unity, courage and above all solidarity."

Rescuers arrive at the area where bodies were found. ( Reuters: Alkis Konstantinidis )

It was unclear how many people remained unaccounted for as coastguard vessels combed beaches to find any remaining survivors, with military hospitals on full alert, a government spokesman said.

One of the youngest victims was thought to be a six-month-old baby who died of smoke inhalation, officials said. Of the 156 people injured, 11 were in intensive care, they added.

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

The fire in Mati village, 29 kilometres east of Athens, devastated the area.

"Mati doesn't even exist as a settlement anymore," one woman told Greece's Skai TV.

"I saw corpses, burned-out cars. I feel lucky to be alive."

Mati is in the Rafina region which is popular with tourists, particularly pensioners and children at holiday camps.

A firefighter wears a flame-resistant uniform as wildfire burns in the town of Rafina. ( Reuters: Costas Baltas )

'An extreme situation': People flee to beaches

The Government sought international assistance to cope with the fires, which have destroyed dozens of homes, burned cars and prompted residents and tourists to flee to beaches east of Athens for dramatic rescues by boats.

Greece said Cyprus offered to send firefighters and Spain has offered water-dropping aircraft.

Firefighters, soldiers and local residents carry a hose as a wildfire burns in Rafina. ( Reuters: Costas Baltas )

Prime Minister Alexis Tsipras cut short a visit to Bosnia on Monday and returned to Athens to preside over an emergency response meeting with fire chiefs and government officials.

"We are dealing with something completely asymmetric," Mr Tsipras said.

"It's a difficult night for Greece."

Winds reached 80 kilometres per hour as authorities deployed the country's entire fleet of water-dropping planes and helicopters to give tourists time to escape.

Military drones remained in the air in the high winds to help officials direct more than 600 firefighters below.

Hours after the blaze began, flecks of ash swirled down onto central Athens. ( Reuters: Alkis Konstantinidis )

A senior fire chief went on state TV to appeal to people to leave the area of Kineta west of Athens after some tried to stay on their properties.

"People should leave, close up their homes and just leave. People cannot tolerate so much smoke for so many hours," Achilleas Tzouvaras said.

"This is an extreme situation."

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

The main Athens-Corinth motorway, one of two road routes to the Peloponnese peninsula, was shut and train services were cancelled.

"We were unlucky. The wind changed and it came at us with such force that it razed the coastal area in minutes," said Evangelos Bournous, mayor of the port town of Rafina, a sleepy mainland port that serves Greek holiday islands.

The dock area became a makeshift hospital as paramedics checked survivors when they came off coast guard vessels and private boats.

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

A witness told Reuters they saw at least four people dead on a narrow road clogged with cars heading to the safe haven of a nearby beach.

Dozens of people scrambled into the ocean as the blaze raged close to the shore, and they were picked up by passing boats.

A man walks among burnt cars following a wildfire at the village of Mati. ( Reuters: Alkis Konstantinidis )

Fires popping up across the country

The first major fire broke out in a pine forest near the seaside settlement of Kineta, 50 kilometres west of Athens between the capital and Corinth.

At least 220 firefighters were on the scene there while five water-dropping planes and seven helicopters were fighting the blaze from the air.

Local communities were evacuated and the blaze shut down a nearly 20-kilometre section on two highways linking the Peloponnese with central Greece.

Thick smoke reduced visibility on the highway to mere metres.

Several houses were in flames, footage from the Greek TV station Skai showed.

Fires fanned by gale-force winds are raging through pine forests and seaside settlements near Athens. ( AP: Thanassis Stavrakis )

Some residents used garden hoses to try to save their properties while others escaped in cars and on mopeds.

Hours after the blaze began, flecks of ash swirled down onto central Athens.

The second major blaze broke out on Monday afternoon in the Penteli and Rafina areas north-east of Athens.

Children's summer camps and a seaside resort for military officers were evacuated, as well as residences in the area.

Residents are fleeing their homes as a swift-moving fire churns out smoke, turning the sky orange over Athens. ( AP: Thanassis Stavrakis )

There was no official figures on how many people were evacuated overall.

Rafina Mayor Vangelis Bournous said he believed about 100 houses in the area had been burned. The fire service was not able to confirm the figure.

A third fire burned farmland and woods on the southern island of Crete, while in northern Greece a forest fire in the area of Soufli was being battled by 50 firefighters.

The fire department said three fires also broke out in the area of Corinth in southern Greece.

It was not immediately clear how any of the fires started.

Forest fires are common in Greece during the hot, dry summers and the country has been facing high temperatures recently of up to 40 degrees Celsius.

Authorities have declared a state of emergency in the greater Athens area. ( AP: Thanassis Stavrakis )

AP/Reuters