The protest followed a series of rallies marking a month's passing since the disaster, the nation's worst in a generation.

Both the central and regional governments have come under fire for the response to the October 29 catastrophe, which wrecked homes, shops and swept away cars by the thousands.

Chanting slogans calling for Valencian leader Carlos Mazon -- accused of raising the alarm too late -- to resign or face jail, the demonstrators marched through Valencia's city centre.

"What went wrong? Incompetence. That's why we are here, because there are a lot of incompetent people who are still being paid," Raquel Ferrandis told AFP.

The 55-year-old teacher from Paiporta, one of the towns worst hit by the rising waters, was carrying a banner in memory of the mother of a friend who died in the floods.

Telephone alerts reached some residents when water was already surging through the streets, while several municipalities went for days without state help and had to rely on volunteers for food, water and cleaning equipment.

Carrying a banner slamming the regional president, 62-year-old teacher Maribel Peralta declared herself "very indignant".

"The people who have lost everything, look at how they live now. The people who have lost their businesses, look at how they live now. The aid is not coming," the Valencia resident said.

For the time being, Mazon has ruled out resigning.

The demonstrators also criticised the central government of socialist Prime Minister Pedro Sanchez, accused of not being more decisive in its handling of the response.

"These politicians are killing the people," one of the posters at Saturday's march read.

Disaster management is the regional administrations' responsibility in Spain's highly decentralised system, but the central government is allowed to furnish regions with resources and even take control in extreme cases.

Mocking the alert issued by Valencia 12 hours after Spain's weather agency raised the rain and flood alarm to the highest level, the demonstrators blared out alarms from their phones and broke out into chants of "murderers, murderers".

"If people had been warned in good time, if they had the means they have, this would not have happened," said Juan Carlos Ribes, who came to demonstrate from a municipality some 50 kilometres (30 miles) to the south.

"Everything else is an excuse," the 58-year-old civil servant added.