Paris, Apr 18 (IANS): Prosecutors investigating the causes of the inferno that ripped through the 850-year-old Notre Dame Cathedral in Paris have questioned construction workers and security staff, as more details have emerged about the effort to contain the blaze, the media reported.

Ten people were interviewed by criminal investigators on Wednesday, the Paris Prosecutor's Office said, adding that interviews would continue on Thursday, CNN reported.

"Tomorrow new witnesses will be heard as well as people already interviewed for further information," the prosecutor's office said.

Following the disaster on Monday evening that destroyed the Cathedral's spectacular Gothic spire and its wooden roof structure which dated back to the 13th century, the office had said 30 employees at the Paris landmark had been questioned.

It also said that in addition to interviews, forensics teams and the central laboratory for the police department had been able to access some areas of the site and begin inspections. Officials are continuing to pursue the theory that the cause of the fire was accidental but have not ruled out other scenarios at this stage.

"While the prosecutor's office does not rule out any hypothesis, we remind that at this stage, nothing in the investigations highlights a criminal origin. Accidental causes remain our privileged lead," the office added.

The Paris fire service, meanwhile, said the nine-hour battle to save the building was one of the most complex it had ever undertaken. At one point, it was feared that the entire structure might be lost.

"If the flames had actually got to the timber frames of the belfries then we would have lost the cathedral completely because it would have led to a chain reaction of collapse," said Gabriel Plus, a spokesman for the fire service.

Philippe Demay, deputy chief of the Paris Fire Brigade, told the media on Wednesday that the operation to put out the flames was "complex", and the "most complicated" he had ever encountered, CNN reported.

On Wednesday evening, cathedrals across France rang their bells in honour of Notre Dame, marking two days since the fire.

Bells tolled at 6.50 p.m. across the country acknowledging what the French Bishops Conference described as "a shock that affects far beyond just the Catholics of our country".

As the scale of the damage became clear, investigators said they were determined to get to the bottom of how the blaze started.

"Investigations continue to search for the truth and identify the origins and causes of the fire," the prosecutor's office added.