Rescue workers found the body of a 6-year-old girl at about 6 a.m., and the body of a 7-year-old boy about an hour later, The Charlotte (N.C.) Observer reported.
Lincoln County Emergency Management spokesman Dion Burleson said the children were found under about 24 feet of dirt in an excavated site about 20 miles northwest of Charlotte.
"These are horrific circumstances," Burleson said.
Burleson said the children were playing in a dug out area of the construction site Sunday evening while the boy's father was operating a backhoe nearby.
A wall in the hole collapsed and buried the children.
"There were several thousand pounds of dirt on top of them," said Lincoln County Sheriff David Carpenter.
More than 100 people worked to recover the bodies, Burleson said.
"We worked as if they were alive," Burleson said.
Burleson said the sheriff's office would investigate what exactly happened at the construction site.
"We have not determined what the father was building," he said. "This is a time of grieving for the family. Our investigation will go forward, but we also are allowing the family to deal with what has happened here."