People are reflected in the front window of a flooded bus as water engulfs an interchange of a highway in Elefsina, western Athens. Picture: Petros Giannakouris/AP
People are reflected in the front window of a flooded bus as water engulfs an interchange of a highway in Elefsina, western Athens. Picture: Petros Giannakouris/AP
People look at a flooded bus as water engulfs an interchange of a highway in Elefsina, western Athens. Picture: Petros Giannakouris/AP
People look at a flooded bus as water engulfs an interchange of a highway in Elefsina, western Athens. Picture: Petros Giannakouris/AP
Staff at a car rental store clean up damage in front of a washed up vehicle following a powerful storm on the Greek island of Symi. Picture: Argiris Madikos /Eurokinissi via AP
Staff at a car rental store clean up damage in front of a washed up vehicle following a powerful storm on the Greek island of Symi. Picture: Argiris Madikos /Eurokinissi via AP
A worker tries to clean a sewer as water covers an interchange of a highway in Elefsina, western Athens. Picture: Petros Giannakouris/AP
A worker tries to clean a sewer as water covers an interchange of a highway in Elefsina, western Athens. Picture: Petros Giannakouris/AP
A man walks past a destroyed car following heavy rainfall in the town of Mandra, Greece. Picture: Xinhua/Marios Lolos
A man walks past a destroyed car following heavy rainfall in the town of Mandra, Greece. Picture: Xinhua/Marios Lolos
Locals stand beside their destroyed house following a heavy rainfall in the town of Mandra, Greece. Picture: Xinhua/Marios Lolos
Locals stand beside their destroyed house following a heavy rainfall in the town of Mandra, Greece. Picture: Xinhua/Marios Lolos
Flash floods in the Greek capital's western outskirts turned roads into raging torrents of mud and debris, killing at more than ten people, inundating homes and businesses and knocking out a section of a highway. Picture: Petros Giannakouris/AP
Flash floods in the Greek capital's western outskirts turned roads into raging torrents of mud and debris, killing at more than ten people, inundating homes and businesses and knocking out a section of a highway. Picture: Petros Giannakouris/AP
A man walks on a flooded street in the municipality of Mandra western Athens. Picture: Petros Giannakouris/AP
A man walks on a flooded street in the municipality of Mandra western Athens. Picture: Petros Giannakouris/AP
Red Cross personnel and firemen carry an elderly man to the ambulance in the municipality of Mandra western Athens. Picture: Petros Giannakouris/AP
Red Cross personnel and firemen carry an elderly man to the ambulance in the municipality of Mandra western Athens. Picture: Petros Giannakouris/AP
A man helps another to walk in a flooded street following a heavy rainfall in the town of Mandra, Greece. Picture: Xinhua/Marios Lolos
A man helps another to walk in a flooded street following a heavy rainfall in the town of Mandra, Greece. Picture: Xinhua/Marios Lolos
A man with an umbrella walks next to a washed up truck outside an open air cinema in the municipality of Mandra western Athens. Picture: Petros Giannakouris/AP
A man with an umbrella walks next to a washed up truck outside an open air cinema in the municipality of Mandra western Athens. Picture: Petros Giannakouris/AP

Mandra, Greece - Flash floods killed at least 15 people, made scores homeless and destroyed infrastructure in Greece on Wednesday after a raging torrent inundated two coastal towns west of Athens following a night of heavy rain.

In devastation locals said was unprecedented in scale, an overnight deluge triggered flash floods in the industrial towns of Nea Peramos and Mandra in the foothills of a mountain just west of Athens.

Prime Minister Alexis Tsipras declared a period of national mourning. "These are very difficult moments for Greece. We are living a great disaster," he said in a state address.

"Immediately and without delay support measures will be adopted for households and businesses affected," he said, without going into details.

Residents said they were woken on Wednesday morning by rainwater and mud coming through their homes. As the scale of destruction became clearer during the day, large areas were covered in water and mud. In some areas floodwaters rose to the first storey of small buildings.

"There was just an incredible amount of water which caused raging torrents," said Yiannis Kapakis, the head of Greece's civil protection service.

Torrential rain of this type is uncommon in Greece, where poor infrastructure can leave citizens vulnerable to flooding. It has been raining steadily for about a week, and the country's met office issued a new severe weather warning for Thursday.

Some residents were forced onto rooftops and balconies while cars were thrust onto porches of homes, rammed like dodgem vehicles into tree trunks or tipped onto their side.

"This is a biblical disaster," Mandra Mayor Yianna Krikouki told state broadcaster ERT. "Everything is gone."

The Attica prefecture, the administrative district for both towns, said it would seek assistance from the EU Solidarity Fund, set up to respond to natural disasters. A state of emergency was declared in the region.

"The walls collapsed, the cars were carried away and they broke everything here. There is nothing left," resident Marina Kolia said. "Water is everywhere in the house."

Mandra and Nea Peramos have a combined population of about 20,000. Many Greek housing settlements are built without taking into account town planning regulations.

An Athens prosecutor ordered an urgent preliminary investigation into the deaths and destruction caused and was also investigating possible urban planning offences.

On Tuesday, Greece declared a state of emergency on the eastern island of Symi, just off the coast of Turkey, after a storm swept cars into the sea, damaged homes and cut off electricity and water supplies.