At least 51 people are known to have died after torrential rain caused flash floods in south-eastern Spain, authorities have said.

Rescue efforts are underway as dozens of people are unaccounted for.

The country has been badly hit by heavy rain and hailstorms, triggering rapid flooding across multiple regions.

The president of the Valencia region, Carlós Mazón, said it was “impossible” to put an exact number on the final death toll at this stage.

Footage uploaded to social media shows floodwaters causing chaos, knocking down bridges and dragging cars through the streets. Other video appeared to show people clinging to trees to avoid being swept away.

The Spanish Weather Service reported that Chiva, in the Valencia region, recorded 491mm of rain in just eight hours on Tuesday - the equivalent to a year's worth of rain.

Radio and TV stations have reportedly been receiving hundreds of calls for help from people trapped in flooded areas or searching for loved ones, as emergency services struggle to reach some areas.

Emergency services workers are using drones to search for the missing in the badly affected municipality of Letur, local official Milagros Tolon told Spanish public television station TVE.

"The priority is to find these people," she said.

Local media reported that dozens of people in Valencia spent the night stranded in trucks or cars, as well as on rooftops and bridges, waiting to be rescued.

Spain's state weather agency AEMET has declared a red alert in the Valencia region and the second-highest level of alert in parts of Andalusia.

 It said the area of worst rainfall in the Valencia region was due to to a weather phenomenon called DANA (Depresión Aislada en Niveles Altos).

This is where there is a pool of colder air higher up in the atmosphere. As warm and moisture laden air moves in beneath it the air becomes incredibly unstable, leading to deeper storm clouds and more intense rainstorms.

The floods have caused transport disruption with several flights due to land in Valencia diverted to other cities and others cancelled.

All train services are suspended in the Valencia region, the national rail infrastructure operator ADIF said.

Valencia city hall said all schools and sporting events are suspended on Wednesday, and parks will stay closed.

Spanish Prime Minister Pedro Sanchez said in a post on X he was following reports of missing people "with concern".

He urged people to follow the advice of the authorities, adding that people should "avoid unnecessary trips.