An explosion in a four-storey apartment building in Valladolid, northwest Spain, has killed one woman and injured 12 people, two of them critically.

The blast took place late on Tuesday night in the city’s main residential area. Authorities believe it could have been caused by a gas explosion on the first floor.

“The flames reached the top of the building,” stated the firefighters to the Spanish agency EFE. After the explosion, firefighters had to work all night to try to extinguish the fire that was ravaging the building.

Eyewitnesses explained that, minutes before 11pm a loud explosion was heard, which alarmed the neighbours.

Firefighters arrived immediately and managed to quickly evict them. However, two critically injured people – a man and his son – are recovering in the intensive care unit as they were severely burned.

The garage underneath the building fuelled the ferocity of the fire as eight cars and a motorbike were stored there, so according to firefighters “the fuel load was brutal”.

The acting mayor of Valladolid, Irene Carvajal, confirmed during a press conference that there were only 13 people in the 20-unit building, as “most of the neighbours were on holiday or away”.

Local officials say the building will not need to be entirely demolished. 

Carvajal pointed out that the structure of the old building, which dates to the last century – is “seriously affected”, especially the ground floor area.