At least 51 people have been killed in flash floods sweeping the eastern Spanish region of Valencia following torrential rain on Tuesday that left roads and towns under water, local authorities said on Wednesday.

Rescuers using dinghies worked in the dark to scour the floodwaters, rescuing several people, television pictures from the town of Utiel showed, and emergency services were still working to reach the worst-hit areas.

Valencia regional leader Carlos Mazon said some people remained isolated in inaccessible locations.

"If (emergency services) have not arrived, it's not due to a lack of means or predisposition, but a problem of access," Mazon told a press conference, adding that reaching certain areas was "absolutely impossible."

Dozens of videos shared on social media overnight appeared to show people trapped by the floodwaters, with some climbing into trees to avoid being swept away. In other videos, firefighters could be seen freeing drivers whose cars were stranded in flooded streets in the town of Alzira.

Emergency services in the region urged citizens to avoid all road travel and to follow further updates from official sources, and a military unit specialized in rescue operations was deployed in some places to help local emergency workers.

Spain's state weather agency AEMET on Tuesday declared a red alert in Valencia, a major citrus-growing region, with some areas such as Turis and Utiel recording 200 mm of rainfall. It has since lowered the alert to yellow as the rain had largely stopped.

Trains to the cities of Madrid and Barcelona were canceled due to the flooding, and schools and other essential services were suspended in the worst-hit areas. Lower house Speaker Francine Armengol said Wednesday's parliamentary session would be called off because of the disaster.

The death toll appeared to be the worst in Europe from flooding since 2021, when at least 185 people died in Germany. It is Spain's worst flood-related catastrophe since 1996, when 87 people died and 180 were injured in a flash flood near Biesca in the Pyrenees.

Scientists say extreme weather events in the region are becoming more frequent due to climate change. Meteorologists think the warming of the Mediterranean, which increases water evaporation, plays a key role in making torrential rains more severe.