Thick black smoke was seen billowing dozens of metres into the air.
Speaking to Dantri reporters, a representative from the Hanoi Fire Prevention and Rescue Police Department confirmed that the blaze began around 2 pm on the rooftop of the Viet Tower Building.
Upon receiving the emergency call, multiple fire engines and dozens of firefighters were dispatched.
By 2.40 pm, the fire was largely under control, although smoke continued to rise from the building.
Authorities have not yet released any official information regarding casualties.
Eyewitnesses reported that some individuals experienced smoke inhalation and were assisted out of the building.
As of 3.15 pm, smoke was still seen escaping from the site.
A security guard told Dantri that authorities suspect someone may be trapped inside an elevator.
"The fire caused a power outage, so there is concern that someone might be stuck in the lift. Rescue teams are currently trying to access the area," the guard said.
The building's rear facade was visibly damaged, with large patches of the outer surface peeling off due to the intense heat.
The cause of the fire remains under investigation.
Viet Tower is an 18-storey commercial building with two basement parking levels located at a busy junction in central Hanoi.