Fire crews on Friday picked through a still-smouldering 14-storey apartment block in Valencia, eastern Spain, a day after a blaze ripped through the building killing at least 10 people.

Experts said the building was covered with highly flammable cladding, which could account for the rapid spread of the blaze after it broke out on the fourth floor at around 5:30 pm Thursday.

Investigators have still to determine the cause of the fire.

Film footage showed clouds of black smoke as the flames consumed the high rise of 138 flats in the Campanar district of the Mediterranean port city.

On Friday afternoon, officials updated the death toll, which had previously stood at four.

“We can confirm that following a first inspection, forensic police have found 10 fatalities,” said regional administrator Pilar Bernabé.

READ ALSO: How safe are Spanish buildings when it comes to fire standards? 

It was still not clear if other people were missing, but local officials have not ruled out the death toll rising.

Another 15 people were treated for injuries of varying degrees, including a seven-year-old child and seven firefighters, but their lives were not in danger.

Fire crews on Friday entered the blackened ruin of the residential block, its windows blown out and the once-white facade charred with the residue of smoke and flames.

Prime Minister Pedro Sánchez visited the scene.

He encouraged people to “show empathy, affection and solidarity with the victims, with their families, with those who still do not know exactly what has happened” to their loved ones.

READ ALSO: Do home insurance companies in Spain cover fires? 

Smoke still wafted from the building though it was quickly blown away by strong gusts of chilly wind, which had fuelled the flames and complicated efforts to quench the blaze.

‘A catastrophe’

Local people took stock of the devastation, their faces grim with shock.

“Luckily it was at a time when a lot of people were not home, some were working, others had gone to pick up their kids at school,” said Juan Bautista, a 70-year-old pensioner who was in a wheelchair.

“If it was later, or at diner, there would have been many more fatalities.”

Slava Honcharenko, a 31-year-old Ukrainian, said he knew several families of compatriots who had lived in the building. They had been relocated to a hotel since Thursday night.

“We feel very bad. We know what it is when you lose your house because we experienced this two years ago in Ukraine,” he told AFP.

Spanish media said rescue workers had used drones to locate the dead.

Esther Puchades, deputy head of Valencia’s Industrial Engineers Association (COGITI), told local media the fire had spread so rapidly because the building was covered with highly combustible polyurethane cladding.

The fire, which started in an intermediate floor, spread within minutes to the entire building, said residents.

Sergio Pérez, a 49-year-old driver who lives nearby, said the building burned as if someone had “poured gasoline” on it.

“It’s a catastrophe. Unimaginable. It’s devastating,” he said.

Dramatic rescue

As the fire raged, residents could be seen waiting to be rescued on balconies.

Firefighters used a crane to pluck a father and his daughter from a balcony where they were trapped, an operation broadcast live on national TV.

Onlookers cheered and applauded as they were brought to the ground.

Other dramatic footage showed a man jumping several floors onto an inflatable mat to escape the flames.

Valencia has announced three days of mourning and suspended the start of its month-long annual Fallas festival.

Fuastino Yanguas of the Valencia fire brigade said the material used on the facade of the building must be investigated.

It was, he said, “a factor that contributed a lot” to the lightning spread of the flames, as were the strong winds, with gusts of up to 60 kilometres (40 miles) per hour at the time the blaze broke out.

The fears that polyurethane cladding might have exacerbated the Valencia fire recalled the 2017 tragedy at London’s Grenfell Tower, when a fire killed 72 people in the 24-storey high rise.

The blaze spread rapidly because of the highly combustible cladding on the block’s outside walls.

A public inquiry into the disaster has yet to publish its final report.