The red alarm has been put in place for most of the country, including the west, south and central areas, as the agency is still unable to forecast exactly where the most rain is expected to fall.

Meteorologist Brane Gregorčič said that heavy rain is forecast for the coming three days, with current calculations predicting that the parts put under highest alert will receive the most rain, although expecting regional differences.

Heavy rain is already moving over Italy towards Slovenia and is expected to arrive overnight, affecting the west first before spreading across the country. Isolated storms and strong showers are possible, said Gregorčič.

In the mountainous Posočje area in the north-west, overnight rainfall could reach 100 millimetres, while 50-100 millimetres is expected in other areas put on highest alert.

The Civil Protection and Disaster Relief Service is in a state of full readiness across Slovenia due to the high likelihood of flash flooding and flooding of rivers and creeks, its chief Srečko Šestan told a press conference called by ARSO.

For the time being the alert for rivers has been put on orange, the second-highest level, as ARSO waits for more data on the predicted rainfall for specific areas.

But hydrologist Janez Polajnar told today's press conference that rivers across Slovenia are expected to cause problems and that the whole country should be on alert.

Rivers and creeks in the north-west and west are expected to start swelling in the night to Thursday, while elsewhere this is expected on Thursday and in the night to Friday.

They are expected to reach the highest level on Saturday, when the rain should start to abate, although areas with large quantities of underground water could face flooding well into next week.

Moreover, the country's Geological Institute warned that the rain would cause a risk of landslides, especially in the north-west and western Slovenia. It called on people to stay vigilant.

Slovenia has faced frequent flooding in recent years, with the most recent episode on 22 October affecting vast areas of central Slovenia, including the south-western parts of the capital Ljubljana.