Police spokesperson Kim Bastiaens said it was still too early to give a figure for the number of injured, or determine the cause of the fire.
Reuters saw rescuers lowering residents from the side of the building by rope. Survivors described being trapped inside until police and firefighters arrived shortly after the blaze started in the morning.
Eighty-year-old Jaklien Heeren, who lives on the fifth floor, said she considered herself lucky to escape.
"I tried to go down, I opened the door and I could smell" the fire, she said.
"(I) could see small flames were coming, and then I went out, and from then, I know nothing any more. I went out and I was lucky."
She managed to get her dog out of the building as well, but two of her neighbours were not answering their phones, she said.
Geert Dewulf, who lives on the 10th floor, told Belgian broadcaster VRTNWS: "We tried to get down on our own but we couldn't manage it any more. We barricaded ourselves in our apartment and waited on the terrace. About 10 minutes later, the fire department came to rescue us from the terrace with their fire ladder."
Several fire brigades from different districts were on site, as were ambulances and other emergency crews. Police told residents nearby to keep doors and windows closed to avoid harm from the smoke.
Belgium's Prime Minister Bart De Wever, a former mayor of Antwerp, said on X that his thoughts were with the victims.
Belgium has experienced a series of severe blazes in the past weeks, including one in a warehouse in Brussels.
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