Dozens of firefighters battled an explosion and fire at an apartment building under construction Tuesday afternoon near the St. Johns Town Center.

Jacksonville Fire-Rescue called a second alarm to get additional units to battle the blaze on the five-story building. In all, 60 firefighters responded and put the fire out in about 15 minutes.

IMAGES:  Fire at construction site

Channel 4 meteorologist Richard Nunn said a relatively small fire broke out just before 4 p.m., but a few minutes later there was an explosion.

TownCenterFire8 "There was a rumble on the ground and you could feel a concussion on your chest, then a fireball took off," Nunn said.

Channel 4 quickly received messages and tweets from people at the Town Center and motorists passing on J. Turner Butler Boulevard that saw or felt the blast and fire.

"I was driving on JTB and I saw a helicopter," witness Adam Mobley said. "When I first got here, there was two big explosions and fire was coming out the top of the roof. It was pretty intense and scary."

There were no reports of injuries despite initial reports that there were workers trapped the roof when the fire broke out. Firefighters said the workers had made it to the ground on their own by the time the first engines arrived.

TownCenterFire24 Jacksonville Fire-Rescue spokesman Tom Francis said it appears two 25-pound propane cylinders exploded during the course of the fire, which grew to consume scaffolding set up around the structure.

Francis said the fire started on the roof of the complex, where workers used heating equipment to lay foam flooring down. The flooring was smoldering about 30 minutes after workers left it, and once they were downstairs, the propane tanks exploded.

Samantha Church was eating a late lunch at Brio Tuscan Grille nearby when the explosion happened.

"You could feel the entire restaurant vibrate. It was insane. It felt like a huge bomb went off or something," Church said.

The apartment complex is being built next to Seasons 52, along JTB. Police blocked off many of the roads around the area due to emergency vehicles in the area.

The State Fire Marshal said the cause of the fire was accidental, but did not release any other details. Damage was estimated to be about $80,000.

The Jacksonville Sheriff's Office said it received so many calls to 911 about the fire that some callers may have had to wait unusually long to speak to a dispatcher.

"We apologize for any inconvenience and want to thank the hundreds of callers that responded to this emergency, all within a few minutes of each other," the Sheriff's Office said in a statement.

Duval County emergency communications center receives high volume of calls

The Jacksonville Sheriff's Office Tuesday released the following statement to Channel 4 about the large number of citizens trying to report the fire:

"Due to the volume of calls our 9-1-1 emergency communications center received today, by citizens viewing the fire off J. Turner Butler Blvd. at the Town Center construction site, some callers may have experienced unusually long wait times. We apologize for any inconvenience, and want to thank the hundreds of callers that responded to this emergency, all within a few minutes of each other."

Channel 4 crime and safety expert Ken Jefferson says the experience might help the county become more prepared for future emergencies.