The full extent of the damage to Paris' Notre Dame Cathedral is yet to be revealed.

Parisians are waking up to what's left of their beloved church.

The roof and main spire of the 850-year-old gothic building have collapsed after a fire broke out, but the main structure including the two bell towers appears to have been saved.

Kiwi Architect Mark Burry, who worked on Spain's famous Sagrada Familia, told Larry Williams when it comes to rebuilding it, a lot rides on the interior damage.

"Typically, cathedrals have two structures, they have the roof itself often made from timber, but what you see from inside is stone vaults. If the vaults have collapsed, it would be catastrophic, but if they've been able to keep the worst of the fire away from that, it's probably not as bad as it looks."

He says that the rebuild will be more straight forward now, than it would have been 10 years ago.

"It's very likely that this building would have been completely scanned in 3D. If that record exists, and there was a will to reproduce the building exactly as it was down to the millimetre, they can do that."