Workers at Paris's emblematic Notre-Dame cathedral have one year, starting on Friday, to finish restoring the gothic monument in time for its reopening following a monstrous fire in 2019.

Restoration of the UNESCO-listed building, which usually welcomes some 12 million visitors each year, has hit several snags since people around the world watched in horror as its steeple crashed down in the blaze on April 15, 2019.

But its new spire has started to emerge against the French capital's skyline, and is expected to be fully completed when the city hosts the Olympic Games this summer.

And behind the scaffolding, hundreds of workers are racing against the clock to restore the rest of the cathedral in time for it to reopen its doors to the public on December 8, 2024.

"We're within the timeframe. We're confident and determined to meet the deadline but it remains a day-to-day battle," the civil servant in charge of restoration, Philippe Jost, told BFM TV last week.

President Emmanuel Macron is expected to visit the cathedral on Friday, according to members of his entourage.

The monument's new spire is identical to the previous one, designed by the 19th-century architect Eugene Viollet-Le-Duc.

Its oak structure is to reach its full height of 96 metres (315 feet) by the end of the year. It will then be covered in lead ornaments before the scaffolding is taken down, Jost said.

The frames of the nave and the choir of the cathedral, which were also destroyed, are then due for completion, after which the reconstruction of the roof can begin.

The final stages are to include cleaning the interior -- an area that covers some 42,000 square metres (452,000 square feet) -- and installing new furniture in the autumn.

Six hundreds seminarians from the Catholic Church pose after a prayer service in front of Notre-Dame de Paris Cathedral, in Paris, on Saturday.

The work has been "entirely funded" by $848 million in donations from France and abroad, Jost said.

Craftsmen and women from across France have contributed to Notre-Dame's revival.

A family carpentry workshop in the village of Hagetmau in southwest France, for example, is particularly proud of its contribution.

For its 60th anniversary next year, it will be delivering its most prestigious order yet -- 1,500 chairs for the cathedral.

"We've already done interesting jobs but this is really something else," business owner Alain Bastiat told AFP in September.

Macron initially promised to have Notre-Dame restored within five years, in time for the Paris Olympics.

But rebuilding was delayed for months by decontamination efforts, after more than 300 tonnes of lead from the roof melted in the fire.

Authorities then had to halt work several times over the first winter due to high winds, before France went into lockdown in early 2020 to fight the spread of coronavirus.

Jost took over the job of overseeing the cathedral's rebirth after the former French army chief in charge of the renovation, General Jean-Louis Georgelin, died in August during a mountain hike.

Jost had been Georgelin's right-hand man before the accident.

More than five years after the blaze, three investigating judges are still looking into what sparked it.

An initial enquiry pointed to it probably being an accident, with an electrical fault or a cigarette among the theories.