Guests and hotel management at the Avanti Resort on International Drive worked to pick up the pieces Monday, trying to salvage what they could after a devastating fire, believed to have been sparked by a lighting strike, destroyed the top floor of one of the hotel's buildings Sunday.

Late Monday, the Orange County Fire Rescue's local fire marshal determined that there was no lightening protection system and there is no county code requiring it in the building that was affected.

Since the building was built in 1985, there was also no code requirement to have a sprinkler system.

The Avanti building was renovated in 2013. However, it didn't need to be updated to today's code because the renovations were only cosmetic and not structural, according to code records pulled by the Orange County Fire Rescue.

Orange County fire officials have begun ushering guests who were staying on the first, second and third floors of the building back to their rooms to get their belongings.

But the hotel's roof collapsed, making access to the top floor much more difficult.

For Lauren Robertson, Monday was the last day of her vacation in Orlando. On holiday from England, her relaxing visit ended in a flash.

"We heard this massive bang on the roof, and the roof shook," Robertson said.

Stunned by what they thought was just a loud clap of thunder Sunday, Robertson and her traveling companion went back to packing.

"Then, 10 minutes later, there was this bang on the door and someone shouting, 'Fire on the roof!'" Robertson recalled. "I just grabbed my phone, and everything I've got is what I've got on me, and everything else is in that room."

The roof of Building 2 at the Avanti Resort erupted in flames, but guests in all three of the Resort's hotel buildings were evacuated.

Video shot from the balcony of another I-Drive hotel shows what may have been the lightning bolt that started the fire.

Lightning strikes near the Avanti Resort, Sunday, July 5, 2015, as seen from the Rosen Inn. (PHOTO/Maryann McGeough, Viewer)

"We were only at the room for about 20 minutes," said Nicola Craig, who had arrived in Orlando from Scotland and was told evacuate shortly after checking in Sunday.

Craig said she ran to the parking lot and jumped back in her car.

"You could see the fire spreading and getting worse," she recalled.

An Orange County fire battalion chief said 29 trucks assisted to put out the fire. No one was injured.

As for Robertson, despite trips to theme parks across Orlando, when she steps on a plane Monday evening, "This is what I am going to remember."

Guests said the Avanti has done a very good job of getting them situated in other hotels. We are still awaiting a statement from hotel officials about the damage.

The resort's communications personnel confirmed that an estimated 144 rooms were affected.

The resort has also put the affected guests in touch with the resort's insurance company who is helping guests rebook rooms and take care of property damage claims.

Meanwhile, state fire marshal's officials are investigating the fire, as well as one at the Buena Place Apartments near Disney World on Friday, also believed to have been started by a lightning bolt.

Officials with the Orange County Fire Rescue are determining if the Avanti building had firewalls, which could have helped the fire from spreading so quickly.

The State Fire Marshal's Office was called in to investigate the fire at the Avanti Resort. (PHOTO/David Bodden, Staff)

(PHOTO/Christina Jensen, Staff)