Four of those who died were members of the same family: the mother, the father, a three-year-old girl, and a baby, El Pais reported.
ADVERTISEMENTAt least ten people are now known to have died and 14 others are injured, following a fire at an apartment complex in Valencia on Thursday.
"The worst news is confirmed. The first inspection by the scientific police has located 10 bodies inside the building," Pilar Bernabé, a city official, tweeted on Friday afternoon.
Five people remain in hospital - four of them firefighters. Their condition is described as stable.
High winds and cladding on the building have been blamed for the flames, though authorities have refused to answer questions on the cause of the blaze.
Four of those who died are reported to be a young couple with two children and two elderly people.
Officials say no one else is missing.
Police have begun to examine the interior of the two residential towers that were destroyed by fire, as questions grow about how the blaze spread in a matter of minutes.
It was not immediately known how many people were in the two buildings when the fire broke out, but dozens are believed to have lost their homes and belongings.
The complex had some 140 apartments.
Three days of mourning are due to be held in Spain.
Many fire crews have now departed, but firefighters and forensic authorities continue to search for the last of the missing residents.
Valencia Mayor María José Catalá said that the danger of the 14-story building collapsing and the intense heat from the fire initially prevented emergency workers from getting in to search for possible survivors.
The fire started on Thursday evening, with authorities saying an investigation is underway.
However, it is now clear that the flames engulfed the building rapidly.
Experts said that the building's polyurethane cladding may have contributed to the fire's ferocity.
The vice-president of the Valencia College of Industrial and Technical Engineers, Esther Puchades, who once inspected the building, told the state news agency Efe that when the material “is heated it is like plastic and it ignites."
She said it was the first fire of its type in Spain, but that other blazes involving the material have been similarly destructive in the United Kingdom and China.
The June 2017 fire at Grenfell Tower in London, which also had polyurethane cladding, caused more than 70 deaths.
ADVERTISEMENTCatalá said it was too early to comment on reports that suggested materials used in construction might have contributed.
Puchades said polyurethane was no longer widely used in buildings without extra safety measures to offset its flammability.
The complex in Valencia was finished in 2009.
In a promotional video, the now bankrupt construction company Fbex boasted that it used a new aluminum-based material as part of its façade.
Prime Minister Pedro Sánchez visited the scene, promising support for those affected and expressing gratitude to firefighters and military personnel who worked to extinguish the blaze.
ADVERTISEMENTThe Valencia regional government declared three days of mourning and announced financial aid to cover accommodation, clothing and food.
Residents were housed overnight in hotels or in the homes of relatives and neighbours, authorities said.