"We will continue to watch over any residual pockets of fire and cool down the areas that are still red-hot, like the wooden beam framework", a fire brigade spokesman said in the early hours of Tuesday.
The cause of the fire is not yet known, although the BBC has reported it may be linked to recent renovation works.
Despite the dramatic image of the flaming cathedral, no one was killed.
One firefighter was seriously injured, Gallet said. Firefighters continued working through the night to cool the building and secure the monument, as residual sparks sprinkled down from the gaping hole where the spire used to be.
Nearby buildings were evacuated as fears mounted that the structure could collapse.
For much of the day, flames and thick plumes of smoke billowed from the cathedral, including the bell tower and the spire. The cathedral is considered to be one of the finest examples of French Gothic architecture.
The cathedral's main stone structure had escaped complete destruction by the time the fire came under control.
President Donald Trump, 72, suggested using "flying water tankers" to put out the massive fire at Notre Dame Cathedral in a viral tweet on April. 15, and it didn't take long for many of his followers to mock his words with various memes and other responses.
Local church leaders opened the cathedral for people to visit and pray after the devastating fire.
Nearing midnight, signs pointed to the fire nearing an end as lights could be seen through the windows moving around the front of the cathedral, apparently investigators inspecting the scene.
Alain Faubert, the auxiliary bishop of the Archdiocese of Montreal, said whenever he goes to Paris he makes a point to stop by the cathedral. "Fluctuat NEC mergitur", she tweeted.
As the famed Cathedral of Notre Dame caught fire in Paris Monday, people in France are grieving.
He said that "starting tomorrow", he would launch an global appeal for the restoration of the beloved church. "It's a huge monument and a huge part of Paris's history". The place where we survived epidemics, wars, liberation. Situated on the Ile de la Cite, an island in the Seine river, its architecture is famous for, among other things, its many gargoyles and its iconic flying buttresses. About 12 million people visit Notre-Dame each year.
Most of the original stained glass windows were long ago destroyed, according to Cohen. Its priceless treasures also include a relic, the crown of thorns, which is only occasionally displayed, including on Fridays during Lent.
Father Tom Willis, of the Cathedral Basilica of St. Augustine, told News4Jax that it is heartbreaking to know the blaze damaged one of the greatest architectural treasures of the Western world, one of the world's most famous tourist attractions and home to incalculable works of arts.
European Council President Donald Tusk sent his condolences to the people of Paris.
U.S. President Donald Trump, speaking at the start of an appearance in Minnesota, spoke of the "terrible, awful fire" that devastated "one of the great treasures of the world".
But after witnessing Notre Dame in person, she says she realizes how profound losing the cathedral would be for Paris and for the rest of the world. A message of support has been left at the altar in Boston as a show of solidarity.