They caused chaos on the roads, cutting public transport and prompting the Clariano river to burst its banks, flooding homes and causing the evacuation of surrounding areas, the emergency services said.
Footage shared by the local AVAMET weather service showed cars being swept away in fast-flowing water in Moixent, and torrents of water engulfing the nearby town of Ontinyent, which borders the Clariano and saw its heaviest rainfall since records began in 1917, the agency said.
With the region on red alert, regional authorities said they had ordered the closure of schools in 84 municipalities, affecting more than 255,000 pupils.
Torrential rain and high winds were continuing to batter southern Valencia and northern Alicante and would likely continue into Friday, the national AEMET weather service said.