If the Contractors had already started work they should be liable. Most likely it would have been something they did that caused it and should be held responsible. Whether a accident or not they should have insurance and be forced to pay for their negligence. If they had not started their work yet then the Company should be liable.
While it is unclear how the fire started, according to news reports, it should come down to who is seeking profits once the Waterfront development is completed. Those who commissioned the apartments are to be responsible for all damages. The contractors, unless the fire is result from faulty construction, should not be held responsible since they do not own the rights to the Waterfront development.
Who should pay for the damages due to fire really comes down to who is at fault. If the contractor is at fault then they should be responsible for paying to repair the damages. If no one is at fault, liability should fall to the property owner to take care of the damages.
I believe the contractors that were hired should have to pay for the damages when a construction site goes up in flames. Companies hire construction firms to take on the responsibility and they pay them to do their job correctly. When these mistakes happen they affect the land, neighborhood, and the company who commissioned the building.