Six people, including an infant, were hurt when they jumped from a second-story window to escape a smoky fire that swept through a south Minneapolis apartment building on Tuesday afternoon, a city fire official said.

Assistant Minneapolis Fire Chief Bryan Tyner said the six victims were hospitalized with injuries and possible smoke inhalation while fleeing the blaze, which burned through the first two floors of the three-story apartment building. One of the adults was in critical condition with injuries "apparently sustained from getting out of the building," Tyner said.

The fire began on one of the floors of the boxy brown-brick apartment complex in the 3200 block of Portland Avenue S., but its cause remained unknown Tuesday night, Tyner said. He estimated that at least 15 people were displaced by the blaze, which comes two days after a fatal house fire in the Cooper neighborhood.

Tyner said it was "hard to say" where the fire originated, because "there was fire on the first and second floor."

Thick black smoke billowing from the second story greeted firefighters when they responded to the scene sometime around 3 p.m., he said.

It took firefighters about 40 minutes to contain the two-alarm fire, Tyner said. At its height, about 35 firefighters and nine trucks battled the blaze on a leafy residential block in the Central neighborhood. None was injured, officials said.

Firefighters returned to the scene Tuesday night to deal with rekindled flames at the unit where the fire started.

According to city housing records, the 53-year-old building has 10 residential units: eight one-bedrooms, two two-bedrooms and an efficiency apartment.

Libor Jany • 612-673-4064 Twitter:@StribJany