The head of Spain's eastern Valencia region admitted on Friday to "mistakes" in handling the country's deadliest floods in decades that killed 216 people there and apologised.

The October 29 disaster claimed 224 lives nationwide. The floods wrecked infrastructure, gutted buildings and submerged fields.

The final bill is expected to soar to tens of billions of euros.

"I'm not going to deny mistakes," Carlos Mazon told Valencia's regional parliament, adding he was "not going to shirk any responsibility."

As the head of the regional government "I would like to apologise" to those who "felt" that "the aid did not arrive or was not enough," he added.

As he spoke, dozens of protesters gathered outside the building, jeering and chanting slogans demanding his resignation and calling him a liar.

Almost half the people killed in Valencia were 70 years old or older and 26 were foreigners, including two Britons.

Outrage at the authorities for their perceived mismanagement before and after the floods triggered mass protests on Saturday, the largest in Valencia city which drew 130,000 people.

Several carried placards that read: "Our hands are stained with mud, theirs with blood."

Critics have questioned the efficiency of the Valencia region's alert system. In some cases, residents were only contacted by telephone when floodwater was already gushing through towns.

The emergency alert was only sent after 8 pm, nearly 13 hours after the state weather agency warned of the risk of "very intense" rain.

The head of Valencia's emergency department admitted she did not learn it was possible to send such warnings until the evening of the first day of the floods.

Under Spain's decentralised system of government, regional governments lead disaster response.

Spain's Socialist-led central government has said Mazon's administration, run by the conservative Popular Party (PP), bore responsibility for not issuing the alert earlier.

Mazon has also come under fire for having been missing for several critical hours on the afternoon of the disaster when it was already raining heavily.

In response to repeated questions for explanations for his absence, he finally admitted he had been having lunch with a journalist to offer her the directorship of the regional television station.

Many residents have complained they were left without food and water for days and had to rely on aid provided by volunteers instead of the government. (AFP)