"Notre-Dame is our sister, it is so sad, we are all mourning - Parisians, French people, tourists, the Chinese, the whole planet", he said.
Construction on Notre Dame - French for "Our Lady" - began in the 12th century and continued for almost 200 years.
The impressive organ dates to the 1730s and was constructed by Francois Thierry.
Paris Deputy Mayor Emmanuel Gregoire described authorities' "enormous relief" at the salvaging of pieces such as the Crown, which were transported to a "secret location" after the fire.
Despite the loss of the spire, the cathedral's iconic twin bell towers remained intact on Tuesday morning along with a number of priceless treasures, including an 18th-century organ and the purported Crown of Christ.
The Foreign Ministry in Cairo also expressed "great regret and pain" over the fire, citing Notre Dame's "historical and culture value" for France and world heritage.
Smoke billows as flames burn through the roof of the Notre-Dame de Paris Cathedral on April 15, 2019, in the French capital Paris.
Funding for the reconstruction of Notre Dame is piling up at a spectacular rate, with two of France's richest families together quickly pledging 300 million euros.
The 56-year-old's father is French billionaire businessman François Pinault, who owns the worldwide luxury group Kering that controls a number of designer businesses including Gucci, Saint Laurent and Balenciaga.
His final message to his "Christian brothers" was that they "could have confidence because this was God's will and maybe God will help us rebuild it (Notre Dame)".
"We had lost it 50 years ago".
Specialised craftsmen and rare materials are expected to be needed to restore Notre Dame, which is seen as an emblem of France and, more broadly, a symbol of Western civilisation that has survived revolutions and war.
Parliament President Antonio Tajani invited European Union lawmakers, meeting in Strasbourg, France, to contribute their day's salary to help finance reconstruction.
A spokesman for Paris firefighters says that "the entire fire is out" at Notre Dame cathedral.
Gabriel Plus said Tuesday morning that emergency services are now "surveying the movement of the structures and extinguishing smoldering residues". The end of the fire doesnt mean the edifice is totally saved. Two French billionaires have already pledged a total of 300 million euros toward the cathedral's reconstruction.
The Pinault family's earlier 100 million-euro donation was widely reported by French media. The St. Boniface Cathedral fire was sparked in the attic by one of the workers repairing the roof.
The official said investigators had now questioned about 30 people, who were mostly employees working on the renovation of the monument.
The week before the fire, religious statues set atop the cathedral were removed for the first time in more than 100 years as part of the restoration project.
"The task is - now the risk of fire has been put aside - about the building, how the structure will resist", said Junior Interior Minister Laurent Nunez in front of the cathedral.