France celebrated the re-opening of the newly restored Notre Dame cathedral on Saturday at a special church service that featured a standing ovation for the firefighters who saved the 12th-century landmark during a 2019 blaze. 

A two-hour service attended by incoming US president Donald Trump among other world leaders began with the archbishop of Paris knocking on the doors of the cathedral three times.

"Notre Dame, model of faith, open your doors to bring together the far-flung children of God in joy," archbishop Laurent Ulrich commanded, banging with a wooden staff crafted from a roof beam that survived the inferno five years ago.

Trump was seated on the front row as guest of honor next to French President Emmanuel Macron, with he and other invitees marveling at the freshly cleaned walls, new furniture, and state-of-the-art lighting installed as part of the overhaul.

In a short speech, Macron expressed the "gratitude of the French nation" for the restoration work, achieved at frenzied speed over the last five years.

France had "rediscovered what great nations can do — achieve the impossible," he said.

'Merci'

One of the most moving moments came when firefighters in their protective workwear walked through the congregation to thunderous applause as the word "Merci" ("Thank you") was beamed on the intricate facade and famous belltowers of the Gothic masterpiece outside. 

Small crowds of Parisians and tourists braved wet weather and high winds on the banks of the River Seine to witness the renaissance of a monument which came close to collapsing due to the intensity of the flames that toppled its roof and spire.

"I find it really beautiful, even more so now that the spire has been restored," Marie Jean, a 27-year-old dentist from southwest France, told AFP outside. 

The reconstruction effort cost around 700 million euros ($750 million), financed from donations, with the re-opening achieved within a five-year deadline despite predictions it could take decades.

Workers had to overcome problems with lead pollution, the Covid-19 epidemic, and the army general overseeing the project falling to his death while hiking in the Pyrenees last year.

Saturday's service featured classical music, the cathedral's choir as well as some frenetic organ-playing during the "re-awakening" of the 8,000-pipe instrument which is considered the voice and soul of the cathedral.

'World going crazy'

Held up as an example of French creativity and resilience by Macron, Notre Dame's renaissance at a difficult time for the country.

The sense of national accomplishment in restoring a symbol of Paris has been undercut by political turmoil that has left France without a proper government since last week when prime minister Michel Barnier lost a confidence vote in parliament. 

Macron is hoping the re-opening might provide a fleeting sense of national pride and unity — as the Paris Olympics did in July and August.

He scored a major coup by attracting Trump along with around 40 heads of state and government, including Ukrainian leader Volodymyr Zelensky, who was given a round of applause as he entered Notre Dame.

Macron hosted three-way talks with Zelensky and Trump at the presidential palace shortly before the ceremony, with future US military support for Ukraine's war effort against Russia's invasion expected to have been discussed.

Trump has vowed to end the nearly three-year Ukraine war when he takes office on 20 January, sparking fears in Kyiv that he will force Ukraine to make territorial concessions to Russia.

"We all want peace. But it is very important for us... that the peace is just for all of us and that Russia, (Russian President Vladimir) Putin or any other aggressor has no possibility of ever returning," Zelensky said according to the presidential website.

One surprising absentee on Saturday was Pope Francis, the head of the Catholic Church.

He sent a message addressed to the French people and weighed into a row about whether the place of worship and tourist attraction should remain free to enter.

The "immense" numbers set to visit Notre Dame should be welcomed "generously and free of charge," he said, clearly opposing a proposition from the French culture ministry to charge for entry.

The exact cause of the 2019 blaze has never been identified despite a forensic investigation by prosecutors, who believe an accident such as an electrical fault was the most likely reason.

On Sunday, the first mass with hundreds of bishops and priests will take place at 10:30 AM (0930 GMT), followed by a second service in the evening at 6:30 PM which will be open to the public.