Spanish Prime Minister Pedro Sanchez offered his condolences to the families of the dead and the injured
At least three people were killed on Wednesday when a huge explosion ripped through a building in Madrid, with officials confirming it was caused by a gas leak.
Images from the scene showed the walls on the top four or five storeys of the residential building in the heart of the La Latina neighbourhood had been blown out, with vast quantities of debris spreading far and wide.
Government representative Jose Manuel Franco told Spain's public television that the blast occurred as a team of workmen were repairing the building's boiler.
Speaking at the scene, Mayor Jose Luis Martinez-Almeida said an 85-year-old woman had died along with a man whose age was not immediately clear, while the third victim was still "under the rubble."
Bulgaria's foreign ministry announced on late Wednesday a 47-year-old Bulgarian man was among those killed.
Another 11 people were injured, one of whom was in serious condition. Church sources told AFP it was a recently-ordained priest.
Despite the force of the blast, no one was hurt in the elderly care home next door, nor in an adjacent school where tonnes of rubble fell into the playground while the children were in lessons, city officials said.
Wednesday was the first day that schools reopened after a nine-day closure due to the heaviest snowfall in Madrid in 50 years.
"This could have been a massive tragedy," said Martinez-Almeida.
Along the street, at least 15 cars were badly damaged by the force of the explosion, which gutted most of the six-storey residential building.
"I was just leaving a nearby clinic when I heard a very big explosion, it was so big I thought it was a bomb," Valentin Moreno, a 48-year-old salesman, told AFP.
"There were people running and a lot of smoke and when I got there, I saw the building's facade had been completely destroyed."
Franco confirmed it was a "gas explosion" and said there were three dead and one missing, indicating the toll could rise further.
Hundreds of police and rescuers filled the streets around the building, which the archdiocese said housed local priests who worked in the area.
'Pray there are no victims'
"Please pray there are no victims," tweeted the Virgin de la Paloma parish church, saying "one lay person has not been found.”
"These were the living quarters for the local parish priests. They are being treated by the ambulance crews and out of danger," it said.
The head of the elderly care home next door said there were no injuries among staff or residents.
"There were just over 100 people inside at the time," Antonio Berlanga, director of the four-storey Los Nogales La Paloma residence, told Spanish public television.
Nine fire crews and 11 ambulances were dispatched to the scene, which was completely closed off to traffic and pedestrians, an AFP correspondents said.
Three hours after the explosion occurred, smoke and flames could still be seen emerging from the building as a police helicopter flew overhead, he added.
Aerial footage released by police appeared to show that the top four or five floors had been completely blown out, with the blast also bringing down the wall of a building in Puerta de Toledo square, some 50 metres away.
Spanish Prime Minister Pedro Sanchez, offering his condolences to the families of the dead and the injured. "Unfortunately, we are mourning the death of several people in the explosion on Calle Toledo," he said on Twitter