Arson is suspected in an apartment fire in south Minneapolis that sent some people inside fleeing for their lives from a second-floor window, authorities said Thursday.

An adult was hospitalized in critical condition after being among those who jumped to safety Tuesday afternoon from the three-story building in the 3200 block of Portland Avenue S., according to Assistant Fire Chief Bryan Tyner.

In all, an infant and five other people suffered injuries or smoke inhalation, Tyner added. Up to 20 others got out unscathed, he said.

The fire started in a first-floor hall, “raising eyebrows” of arson investigators, Tyner said. “There’s not much there to start a fire,” he said.

It took firefighters about 40 minutes to initially contain the blaze, Tyner said. Firefighters returned Tuesday night to deal with rekindled flames.

According to city records, the 53-year-old building has 11 units: eight with one bedroom, two with two bedrooms and an efficiency.