At least 158 ​​people have died in Spain's worst flooding disaster in generations as rescue workers struggle to find survivors.

On Thursday, more than 1,200 workers were dispatched to the rescue mission with the assistance of drones as rains continued to threaten parts of the country.

“The most important thing right now is to save as many lives as possible,” Prime Minister Pedro Sánchez told victims during a visit to affected communities.

But in some of the cities hardest hit by Tuesday night's floods, people had to dig their bodies out of the mud and rubble.

At least 155 deaths were recorded in Valencia, two more were recorded in Castile-La Mancha in the west of the province and another, a Briton, in Andalusia.

At least 40 deaths have been recorded so far in the town of Paiporta in Valencia, where a river overflowed its banks.

“We all know someone who has died,” said pharmacist Miguel Guerrilla, standing in front of his pharmacy covered in thick mud.

“It's a nightmare.”

On Thursday, the BBC watched undertakers and hearses remove bodies from the street, while cars swept away by the storm surge were piled on top of each other on surrounding streets.

Motorists have told how terrifying it was to be caught up in the tidal waves on Tuesday that turned highways and streets into rivers – with many who survived climbing trees or bridges to escape.

Officials did not provide details on the number of people still missing, but said there were “many” as the death toll rose by another 60 on Thursday.

More than 90 deaths were recorded on Wednesday alone, immediately after the torrential rains and flash floods that mainly affected Valencia and Castile-La Mancha and as far south as Malaga.

According to Spanish weather agency Aemet, the equivalent of a year's worth of rainfall fell in just eight hours in the town of Chiva, near Valencia.

As more rain warnings were issued for the south and east of the country on Thursday, King Felipe VI warned that the emergency was “still not over” and Prime Minister Sánchez urged citizens to seek shelter if necessary.

Meanwhile, in flood-hit areas, hundreds are sheltering in makeshift shelters and beginning the slow, arduous task of clearing roads and restoring homes and businesses.

Many roads and the rail network connecting Valencia to the rest of Spain remain cut off.

Spain began an official three-day period of national mourning on Thursday, with flags on government buildings flown at half-mast and minutes of silence observed.

Public anger is growing over the apparent failure of a developed European country to warn many communities of the risk of flooding in a timely manner.

Questions have been raised as to whether civil protection services issued warnings too late.

The civil protection agency, which is deployed in the event of nationwide disasters, only issued an alarm on Tuesday evening at 8:15 p.m. local time, when several towns in Valencia were flooded for hours.

Authorities described the rains and flooding as “unprecedented.”

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.

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.

“There is no doubt that these explosive downpours have been exacerbated by climate change,” said Dr. Friederike Otto of Imperial College London, who leads an international group of scientists trying to understand the role of warming in such events.

The death toll from floods in Spain is at its highest since 1973, when at least 150 people were estimated to have died in the southeastern provinces of Granada, Murcia and Almeria.