Aug. 2 (UPI) -- A natural gas explosion Wednesday heavily damaged a private Minneapolis high school -- leaving two people dead and nine injured, fire and school officials said.
The explosion occurred just before 11 a.m. at the Minnehaha Upper School, a Christian private school, the Minneapolis Fire Department posted on Twitter.
Contractors doing work on the building ruptured a gas line that caused the explosion, police told WCCO-TV.
The news station reported the school's business office assistant, Ruth Berg, died in the blast.
Assistant Fire Chief Bryan Tyner said fire crews rescued three people off the roof.
Nine people were taken by ambulances to Hennepin County Medical Center with three in critical condition, four in serious condition and two suffering "very minor trauma, said Dr. Jim Miner, the hospital's chief of emergency services.
One person believed to be missing was found uninjured, though one remains unaccounted for. Fire Chief John Fruetel said the last missing person is believed to be a contractor.
The injuries were described as fractures, cuts and head wounds and no one was being treated for burns, Miner said.
Tyner also said the missing person might not be inside but "could be walking around out here. ... It may take a while."
School was not in session, but cross-country, basketball and soccer players were practicing there. Some players left before the explosion.
"All the windows just kind of burst out, and there was a huge explosion that was so loud it kind of shook your insides," Kylee Kassebaum, a sophomore cross-country runner, told the Minneapolis Star-Tribune. "As soon as we saw it we got in the car, and someone drove away because we didn't know how safe the situation was."
A girls basketball coach described the explosion as sounding like "a large door slamming."
Minnehaha has two campuses -- one for upper grades 9-12 and one for lower grades. The explosion only affected only the upper school, as the other campus is several blocks away, the academy said in a statement.
School starts for all grade levels on Aug. 23.
The school was founded in 1913 and had 825 students enrolled during the 2015-16 school year.
Master Mechanical Inc. was issued a permit in June for "gas piping and hooking up meter" at the address, according to city of Minneapolis records.
Gov. Mark Dayton posted on Twitter that "the state will provide any and all resources necessary to aid first responders in their efforts to ensure the safety of all those impacted by this morning's explosion."