Two dead in natural gas explosion at US school

Illinois: Federal authorities joined the investigation Thursday into a natural gas explosion at a US school that killed two adults and sent students fleeing as a building partially collapsed.

The blast early Wednesday killed a janitor and a receptionist at Minnehaha Academy, a Minnesota private Christian school for grades kindergarten through 12. Nine people were injured. 

All students at the school`s campus in the city of Minneapolis were accounted for, some fleeing the school building just moments before the blast. 

Two of those injured remained in the hospital Thursday, one in critical but stable condition, according to the Hennepin County Medical Center.

The National Transportation Safety Board (NTSB), known for investigating plane and train crashes, but also charged with probing pipeline accidents, sent an investigative team to the school. 

The NTSB`s Christopher Hart told a news conference that his investigators will begin work Friday, and would likely be at the scene for five to seven days.

A final determination as to what caused the natural gas explosion is not expected for some time.

"Typically, we look at a year or so to complete a final report," Hart said. 

The explosion occurred Wednesday morning in the center part of one of the school buildings, where a construction crew was working.

The blast pushed part of the building`s wall outwards, causing the roof to collapse and pancaking two floors into rubble, according to fire chief John Fruetel.

Rescuers pulled the body of the final missing person from the rubble late Wednesday. School receptionist Ruth Berg and janitor John Carlson were killed.

Witnesses told the Minneapolis Star Tribune newspaper that someone warned of a gas leak moments before the explosion.

The few students in the building — school is currently not in session — managed to escape, according to the newspaper.

"All the windows just kind of burst out, and there was a huge explosion that was so loud it kind of shook your insides," student Kylee Kassebaum told the Star Tribune.