Spanish emergency services have recovered the bodies of four people from beneath the rubble of a six-storey building that collapsed in central Madrid while being refurbished into a hotel, local authorities said on Wednesday.

"It is with deep sadness that we confirm that Madrid firefighters have recovered the bodies of the people who went missing after the collapse," Mayor Jose Luis Almeida wrote on X.

The victims have been identified as three men aged between 30 and 50 from Ecuador, Mali and Guinea-Conakry and employed at the site as construction workers, as well as a 30-year-old woman, the renovation project's architect.

Their remains were found early on Wednesday, nearly 15 hours after the collapse of the building's interior structure that left its facade intact, in a search-and-rescue operation in which police and firefighters deployed drones and sniffer dogs. Three other construction workers were injured.

One construction worker named Mikhail was pumping concrete into the building's lower floors and was outside when the collapse occurred. He said he saw a large cloud of dust and immediately sprinted away.

"I was the first to run, I didn't care about anything else. I'll save my life first and, if I can, save others later," he told reporters on Tuesday.

According to Madrid's online registry of buildings under construction the property was built in 1965. It underwent two technical inspections in 2012 and 2022 and was classified as "unfavourable" due to "the general condition of the facade, exterior, partition walls, roof, roof terraces and plumbing and sewage system".

The former office building, located in an area of downtown Madrid popular with tourists near the opera house and royal palace, was being converted into a four-star hotel by developer Rehbilita, according to information on its website. Rehbilita did not respond to a Reuters request for comment.

The property belongs to Saudi-based fund RSR, a real estate investor specialising in high-end hotels and tourist apartments in Spain and Portugal. RSR bought it for 24.5 million euros ($28.5 million) in 2022.