THE mysterious death of a four-year-old Claremont boy during a sleepover at a friend's home is being treated as a "major crime investigation", Tasmanian police say.
Inspector David Plumpton, of Glenorchy police, said the child and his twin brother were staying with a friend on Friday night at a home north of Hobart.
An ambulance was called to the Claremont property early on Saturday morning.
The child's death was being treated as a "major crime investigation", however police were unable to confirm whether there were any suspicious circumstances.
Police had hoped a post-mortem, which was conducted yesterday, would have given a clear indication as to the cause of death, but Inspector Plumpton said investigations were continuing.
"There are some particular events that we've been unable to positively determine between the time the young boy went to the house ... and the time at which the body was discovered," he said.
"We are trying to identify exactly what occurred from the moment that young boy left his home to go and spend the night with friends.
"There are no obvious injuries that would lead you to say `this is the cause of death of that child'."
He said the child's family was "absolutely shattered" by the sudden death, and the other children in the home at the time would be interviewed by police.