At least four people died in a huge fire that ripped through a 14-storey apartment block in Valencia, eastern Spain, and at least 14 were reported missing, with officials warning on Friday that the death toll could rise.

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 (1630 GMT) on Thursday.

Dramatic images showed clouds of black smoke as the flames consumed the high-rise building of 138 flats in the western Campanar district of the port city.

"Four people have died," Jorge Suarez Torres, deputy director of emergency services for the Valencia region, told reporters overnight.

"As of now, we have 14 people who remain untraced," regional administrator Pilar Bernabe added on Friday, stressing that the number could change.

Valencia mayor Maria Jose Catala had said between nine and 15 people were unaccounted for, based on information provided by police and neighbours, while a city hall source had said on Thursday that 19 people were unlocated.

Fifteen people were treated for injuries of varying degrees, including a seven-year-old child and seven firemen.

Six of the 15 were still in hospital on Friday but their lives were not in danger, regional governor Carlos Mazon said.

Officials said 22 teams of firefighters had been called in to battle the blaze.

Suarez Torres said they had not yet managed to get into the building.

"We're trying to cool the facade. That's our goal over the next few hours," he said.

"We can't say when we'll be able to get inside."

- Combustible cladding -

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.

Luis Ibanez, who lives nearby, told TVE he had looked out of a window and seen the flames engulfing the building "within a matter of minutes".

"(It was) as if it was made of cork," he said.

"I couldn't believe what I was seeing. The whole side of the building directly opposite was on fire, from the first floor to the sixth and seventh floor," he said.

"There was a really strong wind and the fire was spreading to the left at a huge speed."

At the time of the fire Valencia was experiencing wind gusts of up to 60 kilometres (40 miles) per hour, according to national weather office Aemet.

Neighbours who gathered outside expressed shock at the scene and the thought of people being trapped inside.

"It makes your hair stand on end, the thought that people are inside and really suffering. It's a disaster because there could be people in there dying," Julia Pascual told AFPTV.

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

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

Other dramatic footage shows a man jumping several floors onto an inflatable mat to escape the raging fire.

- 'It could have been me' -

"It's absolutely horrible. It gives you goosebumps to think about those people inside," said another local, Luis Alberto Clarin, who had just come home from work.

"It could have been me. It could have been my building."

Spanish Prime Minister Pedro Sanchez said he was "shocked by the terrible fire" and was in contact with the mayor and the regional governor "to offer whatever help is needed".

He was scheduled to visit the scene later on Friday.

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

In October, a fire gutted a nightclub in the neighbouring region of Murcia, claiming 13 lives in what was Spain's deadliest nightclub fire in three decades.

The fears of polyurethane cladding exacerbating the Valencia fire recalled the 2017 tragedy at London's Grenfell Tower.

In that incident, a fire at the 24-storey high-rise in west London killed 72 people.

The blaze spread rapidly due to the highly combustible cladding on the block's outside walls. A public inquiry into the disaster has yet to publish its final report.