MINNEAPOLIS (AP) — Officials at a private school in Minneapolis have identified the employee who was killed in a natural gas explosion on campus, as well as a second worker who remains missing.

Minnehaha Academy says Ruth Berg worked at the school for 17 years before she was killed Wednesday in the explosion. The blast partially collapsed a building on the school's campus.

On its Facebook page, the school says Berg "welcomed everyone with a smile and was always willing to go the extra mile to help our students."

The missing employee was identified as John Carlson, a janitor at the school.

School official Sara Jacobson says Carlson graduated from Minnehaha Academy in 1953, and that the school is hoping for a miracle.

A Minneapolis hospital says it is still treating four people who were injured in the explosion. Nine people were initially taken to Hennepin County Medical Center following thel10:30 a.m.explosion that partially collapsed a building on the school's campus.

The Minneapolis Fire Department says the blast was caused by natural gas, and contractors were working on the building at the time.

The school serves students from pre-kindergarten through 12th grade