A view of Notre-Dame Cathedral after a fire devastated large parts of the gothic gem. Benoit Tessier/Reuters

The French prime minister has announced an international architects' competition to rebuild the spire of Notre Dame Cathedral.

Edouard Philippe is speaking following a special Cabinet meeting on Wednesday held by French President Emmanuel Macron focusing on the reconstruction of Notre Dame Cathedral.

Philippe said the competition aims at "giving Notre Dame a spire adapted to techniques and challenges of our times."

He said authorities have no estimation yet of the total cost of the renovation work. Macron said Tuesday he wants the cathedral to be rebuilt by five years.

Philippe said: "This is obviously a huge challenge, a historic responsibility."

The Paris prosecutor's office says investigators looking into the causes of the Notre Dame fire have still not been able to look inside the cathedral, as it remains unsafe.

Investigators will continue with interviews Wednesday, saying the inquiry will go on until prosecutors uncover "the truth and identify the origin" of the blaze. On Tuesday, investigators spoke with around 30 witnesses, including employees of companies involved in the church's restoration and security personnel.

The Czech Philharmonic and other major Czech orchestras will join forces to play a fundraising concert to help restore Notre Dame Cathedral, heavily damaged by a devastating fire.

The Czech Philharmonic says the orchestras will perform Antonin Dvorak's "Stabat Mater" in St. Vitus Cathedral, a Gothic masterpiece, in Prague on Tuesday.

The orchestras want to support France in renovating one of the most important religious buildings in Europe.

Associated Press