Nathan Woessner, the 6-year-old boy who was rescued Friday after being buried for three and a half hours under 11 feet of sand in Michigan City, Ind., is still in critical condition at a Chicago hospital but is expected to make a full recovery.

Nathan, who lives in Sterlin, Ill., fell into a sand hole at the Indiana Dunes National Lakeshore in Michigan City, near Lake Michigan, after a dune collapsed, burying him under 11 feet of sand. The boy was rescued after three and a half hours. University of Chicago Medical Center spokeswoman Lorna Wong said Nathan was “doing well” even though he was listed in critical condition, the Michigan City News Dispatch reported Saturday.

The nature of Nathan's injuries hasn't been reported, but Wong said the 6-year-old did not sustain any that were life-threatening nor any brain injuries.

Nathan’s “parents want to extend their deepest thanks to the Michigan City fire and police departments and all the authorities, private companies and individuals who contributed to the rescue effort. They also ask that people include this little boy in their prayers,” Wong said in a statement.

Ralph Martin, chief of the Michigan City Fire Department, told the Times of Northwest Indiana that the boy showed signs of life as rescuers pulled him from the collapsed sand dune.

"They say he was in pretty good shape. Our prayers are going out to the family and the child," Martin said.

How the dune collapsed is still under investigation, U.S. National Park Service spokesman Bruce Rowe told the Times of Northwest Indiana.

The Mount Baldy portion of the Indiana Dunes National Lakeshore was closed through the weekend as authorities investigate the incident, Rowe said. It’s also possible that the dunes won’t open up until after then if the investigation remains incomplete.

"We will keep it closed as long as we need to for safety reasons," Rowe told the News Dispatch.

It’s also unclear what Nathan was doing when he became trapped under the sand.

“I have never heard of anything like this here or at other sand dune parks," Rowe said.

Wong said Nathan responded to simple commands after being taken to the hospital on Friday. The 6-year-old was described by the News Dispatch as “somewhat sedated.”

Nathan’s family is optimistic that he will recover from his injuries, Michigan City Police Chief Mark Swistek said after speaking with the Woessner clan.

"The father expressed to me that we didn't give up hope," the police chief said. "He wanted people to know that every minute in this rescue made a difference in this child's life."

Michigan