A rural South Dakota community is mourning a family of six found dead in the ruins of their burned home, as authorities investigate what one official described as an unusual house fire.

Hundreds of people turned out for a memorial service at the Christian Reformed Church on Thursday night to remember Scott and Nicole Westerhuis and their four children.

"It's like a bad dream that we can't wake up from," the Rev. Harry Koops told the crowd. "We realize we can't wake up, and that it is our reality."

Firefighters were called to the Westerhuis home, 3 miles south of Platte, about 5:30 a.m. Thursday, after a passer-by reported the blaze. Authorities did not immediately name the fire victims, but Platte-Geddes School Superintendent Joel Bailey said local agencies informed him that the family had perished. He said the children killed were Kailey, a third-grader; Jaeci, a fifth-grader; Connor, an eighth-grader; and Michael, a high school sophomore.

"Their family was inseparable," family friend Kristina Sprik told the Argus Leader. "They did everything together."

Local, state and federal officials are investigating the cause of the fire. Platte Fire Chief Rick Gustad told The Daily Republic newspaper that the house was "pretty well destroyed" when firefighters arrived.

"It's not a real common occurrence to have a fully engulfed structure fire on arrival," Gustad said.

It took three dozen firefighters seven hours to extinguish the blaze, according to Charles Mix County Sheriff Randy Thaler.

About 1,200 people live in Platte, about 110 miles west of Sioux Falls.

"Everyone in the community is affected by this because in many ways, we're a big family," Koops said.

Scott and Nicole Westerhuis both worked for Mid-Central Educational Cooperative, providing speech, language and hearing services to schools. The Westerhuis children participated in several activities including baseball, football, basketball, track, swim team, gymnastics and choir, according to Sprik.