Emergency services said on X that firefighters were working at the scene near the Plaza Mayor, which is popular with tourists, “after the collapse of various floor slabs”.

The central government’s top representative in the Madrid region, Francisco Martin Aguirre, told reporters at the scene that the collapse “caused the different floors to also give way down to the basement of the building”.

“The damage there is very severe, and the possible impact on adjacent buildings is also being analysed,” he said.

Madrid’s municipal police told AFP neighbouring buildings were being evacuated.

The total number of injuries was unclear.

Martin Aguirre said the toll “at the moment is estimated to be around 10, mostly minor, injuries”.

But Inmaculada Sanz, deputy mayor and a top security official at Madrid town hall, later provided a toll of three injured.

The emergency services had also initially reported three injured workers, “none serious”.

Madrid’s mayor Jose Luis Martinez-Almeida said on X that one of the injured workers had been taken to hospital.

Martin Aguirre also reported four missing people, with Sanz adding that they were three men and a woman.

Police working with drones had cordoned off the street, which was full of ambulances and police cars as dozens of onlookers gathered outside, AFP journalists saw.

Milagros Garcia Benito, who works at a hairdresser in front of the building, told AFP there was “an enormous explosion, it blew out the glass and everything.”

“Lots of white dust, you couldn’t see anything. Firefighters and police started arriving quickly,” she said.

Sanz told reporters that “the amount of rubble is very significant” and that the emergency response “will last quite a long time, not only hours, probably a few days.”

The former office building was being reconverted into a hotel, with data on Madrid town hall’s website showing that a permit had been granted in February.

According to the land registry, the building had six storeys with a total surface area of 6,745 square metres.