A second body has been found in the rubble of a collapsed school building in Minneapolis after an explosion killed a school employee and injured several others, fire officials said Wednesday night.

The explosion at the Minnehaha Upper School at approximately 10:20 a.m. caused two floors of the Christian private school to collapse over a sub-basement, Fire Chief John Fruetel said.

Family members and co-workers identified one victim as Ruth Berg, whose body was recovered from the rubble Wednesday afternoon.

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Fruetel said the second body was recovered around 8 p.m. Wednesday. The vicitm was later identified as John F. Carlson, 82, a janitor at the school, the StarTribune reported.

Seven other adults were hospitalized, including three with critical injuries. Assistant Fire Chief Bryan Tyner confirmed that three people had initially been unaccounted for, but one of those people had been located unharmed.

Ruth Berg, a longtime receptionist, was identified as one of the victims of the explosion. (Fox 9)

"This is a day of extreme heartbreak in Minneapolis," the city's mayor, Betsy Hodges, told a news conference Wednesday afternoon. "This school is beloved."

Aerial video footage of the school's campus showed part of a building crumbled, windows in other areas blown out and shattered, and bricks and other debris scattered about. Tyner said three people were rescued from the roof of the building shortly after the explosion.

Sara Jacobson, a Minnehaha Academy staff member, told FOX9 the explosion was "very loud" and the ceiling tiles were falling and the windows were imploding.

Tramon Vanleer, who helps coach a summer program, was in the gym with five students at the time.

"It sounded like a freight door shutting. It sounded like a large door shutting, and at the same time the lights went out and there was some debris that fell from the ceiling, so we just got out as fast as possible," Vanleer told the Associated Press. "It didn't sound that bad on the inside of the gym, but coming outside it was a lot worse."

City records show Master Mechanical Inc. was issued a permit on June 7 for "gas piping and hooking up meter" at the school's address. Ryan Larsen, a company official, released a statement saying the company was monitoring the situation and referred all questions to the Minneapolis Fire Department.

"Our thoughts and prayers are with everyone involved in the incident," Larsen's statement said.

Minnehaha Academy has multiple buildings on its campus. The school said the blast only affected the "upper school," and that all of the students in the building's gym at the time of the blast were OK.

Gov. Mark Dayton released a statement saying his office was in contact with city officials and the state "will provide any and all resources necessary" to help first responders and ensure everyone is safe.

It was not immediately clear how many people were in the building at the time of the explosion. Classes were not in session, but some children were on campus to participate in summer camps.

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The Associated Press contributed to this report.