The staff member in question is likely to face a fine for starting the fire, reports Danish news agency Ritzau.
North Jutland Police confirmed in a statement Thursday that the fire was started by a weed burner.
The handball arena in the centre was damaged in the fire, while the swimming and skating facilities were spared, Ritzau reported on Wednesday.
There were no people in the hall when the fire broke out, but nearby buildings were evacuated.
“These are tragic pictures. It hurts inside, because Gigantium is part of Aalborg's DNA,” councillor Mads Duedahl of the city's Health and Culture Committee told Ritzau Wednesday.
Gigantium's handball arena has previously been used to host the European Championships in the sport – Denmark's second most popular after football – as well as the national final of the competition to represent Denmark in the Eurovision Song Contest.
Nobody was injured in the fire, although one firefighter was taken to hospital for observation, reports Ritzau.
The employee was removing weeds when he discovered that the building had caught fire, police said.
He then contacted fire services.
The employee has now been charged with breaching safety laws and will likely face a fine, according to the report.
Authorities were alerted to the fire at 11:25am on Wednesday. Fire services worked to put out the blaze throughout the afternoon and evening.
Regional firefighting service Nordjyllands Beredskab remained at the site of the fire during Wednesday night.
The fire service told Ritzau on Wednesday that the extent of the damage caused by the fire is less than originally feared.
“The extent of the damage actually looks reasonable considering the sight we met when we arrived at the scene. We initiated a strong response in order to limit damage,” said firefighter team leader Anders Brosbøl.
Photo: Henning Bagger/Scanpix
“There is also water damage caused by all the water we used. But it looks like we will be able to salvage the wooden floor, Brosbøl added.