Large parts of northern and central Slovenia were inundated on 4 August as a huge weather system dumped up to 200 millimetres of rain in just 24 hours, leading to the worst flooding Slovenia has seen in decades.

The mountainous northwest was hit first as floods ravaged Škofja Loka, Idrija, Žiri and Tržič. The waters there started to recede by the afternoon but revealed a trail of destruction as homes were inundated and roads swept away by landslides.

The situation was worst in Škofja Loka, located in a narrow valley fed by the Sora River. Helicopters had to be deployed to airlift people stranded in homes surrounded by water.

Hundreds of buildings were completely flooded in Škofja Loka as well as in Žiri, a town largely located in what used to be a floodplain.

Flooding in Škofja Loka. Photo: Luka Krek/STA

Further east, the Sava, Slovenia's longest river, spilled over in Medvode, and in nearby Komenda and Mengeš small streams surged to flood hundreds of homes.

The northeastern region of Koroška was badly hit as well. A number of areas in Koroška, which was already severely affected by the July storms, were completely cut off by the flooding Meža and Mislinja rivers and landslides.

Some of the main road links have been severed too, including between Dravograd and Maribor, Dravograd and Ravne na Koroškem, as well as between Dravograd and Slovenj Gradec. Roads to the Šalek Valley further south are closed too.

The situation was similar in the Savinja Valley, one of the most flood-prone areas in Slovenia. In the upper Savinja Valley, Mozirje was completely flooded, the water destroying not just homes but a large industrial zone.

Flooding in Mozirje. Photo: Mozirje Fire Brigade

In nearby Nazarje, the main production facility of one of Slovenia's biggest companies, the home appliances maker BSH Nazarje, was under water.

While the waters started to recede in the afternoon, the surge moved downstream towards Celje, a city of 40,000 people, where the evacuation of large parts of the city was ordered.

At least one casualty has been confirmed so far, a woman in Kamnik. Two Dutch tourists were found dead in the mountains near Kranj, but the circumstances of their death have not been clarified yet, and it is believed they may have been struck by lightning.

Thousands of firefighters and relief workers have been deployed across the country. There are no damage assessments so far, but it is believed the damage will be enormous.

Slovenia is regularly hit by floods but they are typically confined to individual regions. This is the first time in decades that so much of the country has been affected at the same time.

While the proximate cause of the floods was the intense rain that fell over 24 hours, this was just the latest major weather system to hit the country since mid-July.

Precipitation in July was double the long-term average in some parts of the country and before the latest rains the soil was already severely waterlogged and water levels were high.

While the focus is currently on saving lives, repairing the damage will take months if not years. The government is due to hold an emergency session tomorrow after Prime Minister Robert Golob cut short his summer holiday. The National Security Council will hold a session as well.