Elizabeth Flores/Star Tribune, via Associated Press

Firefighters worked to put out a fire that injured at least 13 people on Wednesday in Minneapolis.

An explosion and fire on Wednesday ripped through a Minneapolis building that housed 10 apartments and a grocery, injuring at least 13 people, the authorities said. Most of injuries were burns or broken bones suffered by people who jumped — or were blown — out of rooms on the second and third floors.

The cause of the explosion and fire was under investigation, said Robert Ball, the public information officer for Hennepin County Emergency Medical Services. "It will be sometime before they can narrow down a potential cause."

Six of the injuries are critical, Mr. Ball said in a telephone interview. "The nature of the injuries appears to be burns and trauma consistent with a fall from a distance," he said. "We're not certain whether people jumped out of windows, or fell out, or were pushed out by the explosion."

Officials were also trying to determine if all residents had been accounted for, Mr. Ball said. "The intensity of the fire means they have not been able to conduct a complete internal search," he said.

A Minneapolis police officer who first reported the fire said there had been an explosion, Mr. Ball said. A witness at the scene also told WCCO-TV, a local station, that he saw the building explode and three people jump out of windows to flee the flames.

The fire sent flames 20 feet into the air, and thick billows of gray smoke pouring from the roof. About 50 firefighters responded, battling temperatures hovering close to zero that made their work even more treacherous.

The Minneapolis fire chief, John Fruetel, told reporters that nine of the 10 apartments had been occupied, but he said he did not know how many people were living in them. Firefighters experienced "heavy fire" on the second and third floors when they arrived, he said.

"Crews made entry into the first floor of this structure, but conditions became very untenable very quickly," Chief Fruetel said.

Hassan Ali, an interpreter who lives in the neighborhood, said the halal grocery store was popular among Somali-American residents in the area.

A mosque sits behind the grocery store, but it was not clear whether it suffered any damage.