At least 158 people have died in Spain's worst flooding disaster in generations as rescuers battle odds to find survivors.

On Thursday more than 1,200 workers, aided by drones, were deployed to the rescue mission as rains continued to threaten parts of the country.

"Right now the most important thing is to save as many lives as possible," Prime Minister Pedro Sánchez told victims in a visit to affected communities.

But in some of the towns worst- hit in Tuesday night's floods, people were left to the task of recovering bodies from the mud and wreckage.

At least 155 deaths were recorded in Valencia, while another two have been recorded in Castilla-La Mancha to the province's west, and another, a British man, in Andalusia.

In the town of Paiporta, Valencia where a river burst its banks, at least 40 deaths have been recorded so far.

"We all know someone who has died," said pharmacist Miguel Guerrilla, standing outside his chemist shop which has been covered in thick mud.

"It's a nightmare."

On Thursday, the BBC saw undertakers and funeral vans retrieving bodies from the street, while on nearby roads, cars swept away by the storm surge were piled on top of each other.

Motorists have recounted the horror of being trapped by the surging tides on Tuesday which turned highways and streets into rivers - many who survived climbed trees or bridges to escape.

Officials haven't disclosed the number of people still missing but said there are "many", as the toll rose by about another 60 deaths on Thursday.

More than 90 deaths were recorded on Wednesday alone in the immediate aftermath of the torrential rains and flash floods, which largely affected Valencia, as well as Castilla-La Mancha in Andalusia, and as far south as Malaga.

The town of Chiva near Valencia received the equivalent of one year's rainfall in just eight hours according to the Spanish meteorological agency Aemet.

As further rain warnings were issued for the south and east of the country on Thursday, King Felipe VI warned the emergency was "still not over" and PM Sánchez warned citizens to take shelter where necessary.

Meanwhile in flood-affected areas, hundreds are sheltering in temporary accommodation and beginning the slow, arduous task of clearing streets and recovering 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 national mourning period on Thursday with flags at half-mast on government buildings and minutes of silence held.

Public anger is growing over how a developed European country appeared to fail to warn many communities of the flood danger in time.

Questions have been asked over whether disaster management services issued warnings too late.

The civil protection agency, deployed during national disasters, did not issue an alert until 20:15 on Tuesday evening local time, by which time several places in Valencia had been flooded for hours.

Authorities have called the downpours and flooding "unprecedented".

Many factors contribute to flooding, but a warming atmosphere caused by climate change makes extreme rainfall more likely.

Weather researchers have identified the likely main cause of the intense rainfall as a “gota fria” – a natural weather event that hits Spain in autumn and winter when cold air descends on warmer waters over the Mediterranean.

However, the increase in global temperatures had led to the clouds carrying more rain, scientists told the BBC.

The world has already warmed by about 1.1C since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.

“No doubt about it, these explosive downpours were intensified by climate change," said Dr Friederike Otto, from Imperial College London, who leads an international group of scientists who try to understand the role that warming plays in these type of events.

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