Four people have died in the Spanish capital, Madrid, when a multi-story building under construction partly collapsed.

The bodies of two people reported missing were recovered from the building's rubble early on Wednesday morning, Madrid's emergency services said in a post on X.

Rescue workers had recovered two other bodies shortly before midnight. 

Workers from Mali, Guinea and Ecuador were among the dead, according to Spain's EFE news agency. 

At least three people were injured, one of whom was being treated in hospital for a leg fracture.

Too early to know reason for building's collapse

Some 30-40 people reportedly worked at the building, EFE and local media said, which was being renovated to become a four-star hotel.

"Several ceiling structures of the building, which was undergoing renovation, collapsed," Beatriz Martin, spokesperson for the Madrid emergency services, told reporters.

It was still too early to talk about the cause of the accident, Martin said. 

But because it is a workplace accident, Madrid's Judicial Police are "in charge of the incident's investigation," Madrid's emergency services said in another post on X.

Hours before the recovery of the bodies, Madrid's mayor, Jose Luis Martinez-Almeida, said the search for those missing in the rubble a "complex, difficult task," adding that police dogs had been called in to help.

Witness: 'It sounded like a bomb'

Witnesses and passers-by reported hearing a large bang and seeing thick smoke when the building collapsed around 1 p.m. local time (1100 GMT/UTC). 

"It sounded like a bomb," one employee in a nearby bakery told Spanish broadcaster RTVE.

"You suddenly couldn't anything," added a local barman.

Edited by: Wesley Rahn, John Silk