Spain is experiencing its worst flooding disaster in decades, with at least 95 people dead and dozens more missing after heavy rains hit the eastern province of Valencia and beyond.

Torrential rains triggered flash floods on Tuesday that swept away bridges and buildings and forced people to climb onto roofs or cling to trees to survive.

President Pedro Sánchez has declared three days of national mourning as extreme conditions continue and some rescue efforts are curtailed.

There are fears the death toll will rise as “many people are still missing”, the government said.

The flood death toll is the highest in the country since 1973, when at least 150 people were estimated to have died in floods in the southeast.

In his nationwide address on Wednesday, President Sánchez urged citizens to remain vigilant and promised a full recovery. He told the victims: “All of Spain is crying with you… we will not abandon you.”

According to national weather agency Aemet, Chiva, one of the first affected towns near Valencia, reported a year's worth of rain in just eight hours on Tuesday.

While the Spanish army and rescue workers rushed to rescue operations on Wednesday morning – including bringing people to safety from balconies and car roofs – survivors in Valencia reported the horror of the floods on Tuesday evening.

Sudden flooding turned roads and paths into rivers, catching many drivers unprepared.

Guillermo Serrano Pérez, 21, from Paiporta, near Valencia, said the water rushed across a highway “like a tsunami,” forcing him and his parents to abandon their car and climb onto a bridge to escape survive.

Another witness recounted a scene when highway drivers noticed a stream of water coming toward them and formed a human chain to escape along a raised median.

“Thank God no one slipped because if someone had fallen, the current would have carried them away,” Patricia Rodriguez, 45, told El País newspaper.

A resident of La Torre told the BBC that some of his friends had lost their homes and that on Tuesday evening he saw “cars floating in the water” and the tides “breaking through some walls”.

Meanwhile, the mayor of Horno de Alcedo, a town just outside Valencia, told BBC Newshour how water levels rose by more than a meter in just a few minutes.

“The currents were so fast – and we called the emergency services, who started rescuing some people who were up to their necks in water,” said Consuelo Tarazon.

There are widespread allegations in Spain that civil protection authorities were in many cases too slow to issue warnings, resulting in people failing to get off the road or seek higher ground.

The civil protection agency, which responds to nationwide disasters, did not issue a warning until 8:15 p.m. local time on Tuesday evening – but by then Chiva and several other towns had already been flooded for at least two hours.

The regional government of Valencia was also forced to defend its decision to dismantle the Valencia Emergency Unit, set up by the previous government to deal with natural disasters such as floods and forest fires.

Spain sent more than 1,000 soldiers to help with rescue efforts on Wednesday, but many crew members remain cut off from cities by flooded roads and downed communications and power lines.

European Union chief Ursula von der Leyen said she had activated her Copernicus satellite system to help coordinate Spanish rescue teams. Other European neighbors have also offered to send reinforcements.

Earlier on Wednesday, Spain's Defense Minister Margarita Robles said the flooding in the region was “an unprecedented phenomenon.”

Rain eased in the country's central east on Wednesday, but weather authorities warned that rainfall would shift northeast to the Catalonia region. Weather warnings have also been issued in several other parts of the country, urging people to prepare for flooding and seek shelter.

Many factors contribute to flooding, but warming of the atmosphere caused by climate change increases the likelihood of extreme rainfall.

Weather researchers have identified the likely main cause of the heavy rains as “Gota Fria” – a natural weather event that hits Spain in autumn and winter when cold air falls on warmer waters over the Mediterranean.

However, rising global temperatures have caused clouds to carry more rain, scientists told the BBC.

“For every fraction of a degree of warming from fossil fuels, the atmosphere can retain more moisture, leading to heavier showers,” Dr. Friederike Otto of Imperial College London, who leads an international group of scientists trying to understand the role that warming plays in such events.

“No doubt, these explosive rainfall events have been exacerbated by climate change.”

The world has already warmed by about 1.1°C since the beginning of the industrial era, and temperatures will continue to rise unless governments around the world make drastic emissions cuts.