Investigators think an electrical short-circuit was the most likely cause of the Notre Dame Cathedral fire, according to a French judicial police official.
Professional mountain climbers have been appointed to help protect Notre Dame cathedral from potential rain damage.
The team was appointed by the man in charge of a restoration of the Paris landmark after it was ravaged by fire last Monday.
Philippe Villeneuve told the BFM television station said: "The highest priority is to protect the cathedral from the rain to come.
Work to install temporary tarpaulin over the building started on Tuesday. The Met Office has predicted heavy rainfall in the French capital during Wednesday and Thursday.
According to Patrick Chauvet, the rector of Notre Dame, the gothic attraction is not expected to reopen to visitors for five or six years.
But French president Emmanuel Macron has pledged to project to be completed sooner - within five years.
Investigators believe the blaze was an accident. One possibility is that it was linked to renovation work on the site.
Nearly £1 billion has been pledged by donors to rebuild the cathedral. Its roof was destroyed in the fire.
On Monday, approximately 50 people from a French homeless association protested outside, holding placards which read "one billion in 24 hours".
Some chanted: "Notre Dame needs a roof, we need a roof too."
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