France will hold an international architectural competition to decide whether and how to replace the spire of the Notre Dame Cathedral, Prime Minister Edouard Philippe said.

The 93-metre high, lead-covered wooden spire – the work of 19th-century restorer Eugene Viollet le Duc – collapsed into the flames during the Monday blaze that destroyed the cathedral’s roof.

“The international competition will decide whether a spire should be rebuilt, [and] whether the spire designed and built by Viollet le Duc should be rebuilt in the same way, identically,” Philippe said.

Alternatively, the cathedral could be given “a new spire, adapted to the techniques and challenges of our time,” he said Wednesday after a government meeting dedicated to the reconstruction of the cathedral.

President Emmanuel Macron has vowed to have the rebuilding completed within five years. Philippe said that he thought it was “healthy” that the state should “set out our ambitions” for the project.

Asked whether there was any estimate yet for the cost of the reconstruction, Philippe said: “No.”

The Paris prosecutor’s office meanwhile said that investigators probing the blaze had spoken to 30 witnesses on Tuesday and would be questioning more people on Wednesday.

The witnesses include cathedral safety officials and employees of the companies that were working on a restoration project on the roof and spire, the office said.

The investigation is focusing on an accidental cause of the fire, with experts and French media saying it may have been linked to the restoration work.

Scientific experts have not yet been able to enter the cathedral, amid fears that parts of the structure may still be unsafe.

The cathedral’s main religious relics and works of art have been brought to safety in the Louvre Museum, where Philippe said they would undergo an in-depth assessment by experts.

The three great stained-glass rose windows in the cathedral’s west, south and north facades have also survived.

The French government has launched an international appeal for donations. More than 600 million euros (679 million dollars) had been pledged by Tuesday evening.

Journalist and heritage adviser to Macron, Stephan Bern, told broadcaster BFMTV that he expected donations would pass the billion-euro mark on Wednesday.