MADRID, May 22 (Xinhua) -- Two workers were missing and one was injured after the interior of a building collapsed in the center of Madrid on Tuesday.

Rescue services and Spanish national TV station RTVE reported that the inside of the building at number 19 Calle General Martinez Campos' collapsed when the two workers were on the fifth floor.

The online newspaper El Economista informed that work had only recently begun on the building in order to convert it into luxury flats and that the accident was caused when part of the masonry from the seventh floor fell, causing the floors underneath to give way.

Around 20 people were estimated to have been working on the building at the time of the collapse, and one was reported as having been slightly injured.

Emergency Services sealed off the street, with members of the Madrid Fire Brigade and police starting to search for the missing men.

Neighbors interviewed on RTVE spoke of hearing a loud noise and finding the street filled with dust and small pieces of debris in the aftermath of the accident.

"After the first collapse, there have been several partial collapses. The zone is unstable and the buildings on either side (numbers 17 and 21) have been evacuated. The rubble is accumulated on the first floor," confirmed the Madrid Emergency Services in a tweet.