An exceptionally powerful Mediterranean storm from Tuesday unleashed heavy rains and torrents of mud-filled water that swept away people and wrecked homes, with the eastern Valencia region hit hardest.

The body coordinating rescue work in the Valencia region announced that 155 bodies had been recovered there by Thursday afternoon.

Officials in Castilla-La Mancha and Andalusia had announced a combined three deaths in their regions on Wednesday.

With many people still missing and some areas remaining inaccessible to rescuers, government ministers had warned Wednesday's provisional toll of 95 was likely to rise.

"Please, stay at home... follow the calls of the emergency services," pleaded Prime Minister Pedro Sanchez.

"Right now the most important thing is to save as many lives as possible," Sanchez told residents of the eastern Valencia and Castellon provinces.

King Felipe VI warned the emergency was "still not over" and national weather service AEMET put parts of eastern and southern regions on high alert levels for rain on Thursday.

Flags flew at half-mast on government buildings and minutes of silence were observed nationwide at the start of three days of national mourning after Spain's deadliest floods in decades.

Eliu Sanchez, a resident of a suburb of Valencia city, recalled how the merciless currents snatched a man who tried to take refuge on a car.

"I have been told of people who were clinging to trees, but the force made them let go and they were carried away, calling for help. Trucks, everything was going from here to there," said Sanchez, 32.

- 'Catastrophe' -

Emergency services backed by drones and more than 1,200 troops combed mud-caked towns and villages to find survivors and clear roads of debris.

Abandoned vehicles lay piled on top of each other like dominoes and some residents grabbed planks of wood to plough through layers of thick, sticky mud, AFP journalists saw in the Valencia region.

In Paiporta, a suburb of Valencia city at the epicentre of the damage, 27-year-old musician David Romero lamented a "catastrophe".

"Neighbourhood after neighbourhood, street after street, there is not a business standing," he told AFP.

Hundreds of people are being sheltered in temporary accommodation while road and rail transport have been severely disrupted.

It could take up to three weeks to reopen the high-speed line between Madrid and Valencia, Transport Minister Oscar Puente wrote on X.

- 'Nobody warned' -

Scientists say human-driven climate change is increasing the length, frequency and intensity of extreme weather events that are increasingly unpredictable and difficult to control.

The political fallout of the disaster started to rumble on Thursday after doubts were raised about the adequacy of warning systems.

Romero said the warnings in Paiporta only arrived when the local river was already overflowing and catching people off guard in the streets, a complaint echoed by 21-year-old Joaquin Rigon.

"Nobody warned of anything... they took out the owner of the bar here dead, drowned, chaos," Rigon told AFP.

The conservative head of the Valencia region had appeared to shift responsibility to the left-wing central government on Wednesday.

But the interior ministry criticised "erroneous information" on Thursday and said the regions, which have wide powers in Spain's decentralised political system, are responsible for managing civil protection procedures in emergencies.