The fifth floor of the offices - owned by First National Bank - was the suspected origin of the fire.
JMS spokesperson Synock Matobako said they received a call at around 2pm and found that the building had caught fire.
“The fire started on the top floor and it was well alight, while the roof had collapsed,” Matobako said.
“You can see that on the right side of the building the whole top floor has collapsed and we are a bit worried about the structural collapse.
"That is why you saw us moving cars out of the building to make sure that if the building collapsed, nobody would be affected,” he said.
“I can confirm that nobody was injured.”
He said the structural damage caused by the blaze was of concern but said the damage would only be determined after investigators had concluded their task.
Matobako said a search was conducted to determine whether anyone was trapped inside the building before the crew started fighting the fire.
“The fire was still ablaze at the time investigators arrived. The problem is that the fire happened on the top floor which is not stable, so they will not be able to work until the site has been declared safe. We don’t want to put lives in danger by sending them to top floor and they end up falling to the ground floor.”
He did not give a time frame as to when investigations would be concluded.
A construction worker who was repairing the roof said he saw a smoke cloud billowing from the side of the building.
“(It) looked like an electric cable with flames on it which led to a lot of smoke coming out of the building,” he said.
He asked not be named as he is not authorised to speak to the media.
He said a couple of his colleagues attempted to assist them when they heard cries of a fire.
“One of them climbed up with a bucket of water because he thought it was a small blaze but found that about 25m of the roof was on fire and a bucket of water was not going to help,” he said.
An employee who works on the top floor said they were fortunate to have escaped.
Mass pandemonium and chaos followed the discovery of the blaze.
“We first thought (there was) smoke because of the guys who were working on the roof. There was dust before then,” she said.
“We then heard one of them saying it's fire and we needed to evacuate the building.”