At least 10 people were killed, while 13 others were missing after a fire ripped through an apartment building in eastern Spain's Valencia, local authorities said Friday.

Television footage showed the entire facade of the building ablaze as burning segments fell to the pavement below and small explosions were heard inside.

Local media reported several residents calling for help from the balconies of their apartments.

The fire began on the fourth floor of the building in an affluent neighborhood of Spain's third-largest city and spread to other apartments, emergency services said on X.

Ana Mari Gonzalez, who works in a nearby clinic, told state broadcaster TVE that she could see firefighters working to rescue a teenage boy trapped on the building's first floor.

Sixteen firefighting units and five ambulances were deployed at the scene, according to local emergency services. Rescue teams said 19 people were missing.

The deputy head of emergency services in the Valencia region, Jorge Suarez, told reporters that four people had been confirmed dead in the blaze, adding that the building's characteristics did not allow to extinguish the flames inside, with firefighters first attempting to cool down the facade.

Suarez said that there did not appear to be a risk of the structure collapsing for now, but firefighters were nonetheless operating from the outside due to security criteria.

Four of the victims were from the same family - a mother, father, a 3-year-old girl, and a newborn baby, El Pais reported.

Valencian President Carlos Mazon said 15 people were injured, five of whom were firefighters. None are in serious condition.

On Thursday, firefighters were able to rescue two people who were standing on their balconies. A firefighter also had to jump from the second floor, fleeing the flames.

Polyurethane suspected

Experts originally told Spanish media that the buildings were clad with polyurethane - the same material used to insulate the Grenfell Tower in London, which went up in flames in 2017, killing 72 people.

The scenes between the two fires were similar - the buildings in London and Valencia were engulfed by flames within around 30 minutes of the original fires breaking out. Thick plumes of black smoke billowed out.

However, the official body of Valencian architects later denied the building had used the highly flammable material, saying mineral wool insulation was used instead.

Its head suggested the fire spread so quickly due to the air chambers in the building, in addition to strong winds which were also present.

The building was built between 2005 and 2009, according to local media.

Esther Puchades, vice president of the College of Industrial Technical Engineers of Valencia, originally told broadcaster Cadena Ser that polyurethane was likely the cause, which she said can act like a "match" when exposed to a flame.

Later, she said that according to Valencia Plaza, they would have to wait for an investigation to determine the material.

"All signs pointed to polyurethane as causing the voracity of the flames and the color of the smoke," she said. "But in my experience, the facade had some materials with plastic components."

Media reports said that the fire broke out on the eighth floor and spread across the two attached apartment buildings where around 450 people live.

Valencia has declared three days of mourning, which includes suspending the first events of the famous Las Fallas festival.