The civil protection agency, overseen by the regional government, issued an emergency alert to the phones of people in and around the city of Valencia after 20:00 local time (19:00 GMT) on Tuesday, by which time the flood water was swiftly rising in many areas and in some cases already wreaking havoc.
Questions remain about the timing of the alert and whether Spain has an adequate warning system for natural disasters.
Mireia, who lives close to some of the devastation in Valencia, said that people were “not prepared at all”.
“Many people were inside their cars, they couldn’t make it out,” she said. “They were just drowned by the water.”
Thousands of volunteers are currently helping the Spanish military and emergency services with the rescue and clean-up operation, and Valencia’s regional president, Carlos Mazon, said more troops would be deployed.
Spain’s Prime Minister Pedro Sanchez took to social media to express his thanks to volunteers, calling them an “example of solidarity and the limitless dedication of Spanish society”.
He has vowed that his government will do whatever it takes to help those affected by the disaster.
In the devastated town of Paiporta, where more than 60 deaths have so far been reported, residents have expressed their frustration that aid is coming in too slowly.
“There aren’t enough firefighters, the shovels haven’t arrived,” Paco Clemente, a 33-year-old pharmacist, told the AFP news agency as he helped clear mud from a friend’s house.
Dozens of people have been arrested for looting, with one Aldaia resident telling AFP he saw thieves grabbing items from an abandoned supermarket as “people are a bit desperate”.