The explosion, which took place in a building on Toledo Street, caused extensive damage, according to video footage tweeted by Madrid City Hall emergency information service Emergencias Madrid.
At least four floors have been affected by the explosion and firefighters are evacuating people from the building, the service said.
“Different people are treated (for injuries) of different severity,” Madrid Mayor José Luis Martínez Almeida of Madrid told journalists. One has been sent to hospital, he added.
Martínez-Almeida urged caution as authorities continue to get more details after the explosion. “It looks like there has been a gas explosion,” he said.
Police officers are on the scene, a spokesman for the Spanish national police told CNN.
No one was injured in a nearby retirement home and all residents have been evacuated, the mayor said. The director of the Los Nogales residence, Antonio Berlanga, confirmed that story.
This is a breaking news story and will be updated.