Blaze at Paris cathedral being treated as accidental but search of interior yet to take place due to safety risk

French investigators believe an electrical short circuit may have caused the fire at the Notre Dame Cathedral, as police attempt to piece together how the centuries-old world heritage site went up in flames.

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Investigators so far believe there was an accidental cause to the fire that ripped through the gothic architectural masterpiece on Monday night, toppling its spire and destroying most its roof.

Investigators have been questioning cathedral staff, as well as workers who were carrying out renovations. About 40 people had been questioned by Thursday, according to the Paris prosecutor’s office.

An initial assessment of the cathedral was been carried out this week. But investigators have not been able to begin searching for evidence as safety hazards have prevented them entering the charred interior.

A judicial police official told Associated Press an electrical short circuit might have been at the heart of the fire. Investigators are expected to search through the charred cathedral looking to find remains of cables, lights or part of circuitry which might give clues, but DNA evidence could be complex to collect from the large fire site.

Play Video 1:11 Notre Dame Cathedral: before and after the devastating fire – video

Drone imagery has already indicated that the fire broke out at the centre of the roof near the base of the spire, but the exact location has not been established – imagery from the cathedral’s security cameras is being examined.

A team of 60 firefighters are still stationed inside the cathedral to ensure security, as architects and engineers established how the structure can be secured.

The police official would not comment on an unsourced report in Le Parisien newspaper that investigators were looking at whether the fire could have been linked to a computer glitch or the temporary elevators used in the renovation work, among other possibilities. The prosecutor’s office said only that “all leads must be explored”.

The company which put up more than 200 tonnes of scaffolding around the spire for restoration work has said it was cooperating with the police and had no responsibility in the fire. A spokesperson said the police confirmed there were no heatsources on the scaffolding and no soldering work.

With the cathedral likely closed to the public for years, the rector of the Catholic parish that worships there has proposed building a temporary structure on the plaza in front of the landmark. City authorities gave their approval on Thursday “subject to technical restraints”.

“The rector has no cathedral for the moment ... but I’m going to try to invent something,” Bishop Patrick Chauvet said.