As France's Notre Dame Cathedral engulfed in flames, Singapore Prime Minister Lee Hsien Loong was among the first world leaders to express how deeply he was saddened to see the Paris landmark engulfed in flames, especially during the holy week.

"Deeply saddened to see the Notre Dame Cathedral in Paris engulfed in flames. It is particularly poignant that this happened during Holy Week. I share the sense of loss of the French people over the damage to their national monument and the treasures it contained," he wrote on Facebook on Tuesday (April 16).

The Notre Dame was a testimony to world events held in Paris and Europe for more than 850 years and it is part of the heritage of mankind, an expression of the religious faith and human spirit of generations of people who conceived it, built it, and worshipped in it, the prime minister noted. "I hope in time, a rebuilt Notre Dame will fill the Paris skyline."

The the centuries-old Gothic cathedral, ironically featured in Victor Hugo's classic novel The Hunchback Of Notre-Dame, is a Unesco World Heritage site. The fire began in the early evening, burning for hours before it was brought under control.

The flames had engulfed and toppled the spire and the entire roof of the cathedral, except for main bell towers. One firefighter was injured in the incident. French President Emmanuel Macron has vowed to rebuild the cathedral and reports are pouring in that people are pledging funds for the rebuild.

French billionaire Francois-Henri Pinault pledged 100 million euros ($113 million). The CEO of the Kering group, which owns Gucci and Yves Saint Laurent, said the money to completely rebuild Notre-Dame would be paid by the Pinault family's investment firm Artemis.

Key Facts about Notre-Dame de Paris

The construction of Notre-Dame de Paris (Our Lady of Paris) cathedral started in 1163 during the reign of Louis VII and continued into the next century. The dominant bell towers, called "bourdon" and "Emmanuel" were added in 13th century.

Several additions such as the stonework and stained glass of the edifice to recreate images and lessons from the Bible were made in the 17th and 18th centuries. The monument celebrated its 850th jubilee in 2013.

It has 387 steps up to the towers where the gallery of chimeras, mythical creatures greet visitors. The "Stryge" gargoyle atop the cathedral watching Paris with its head resting in its hands gives the monument its unique feature.

Writer Victor Hugo's 1831 novel, The Hunchback of Notre-Dame, depicts Quasimodo, who was feared for his deformity ends up in the succour of the cathedral as a bell-ringer.