An autopsy on the unidentified body of a small child found buried in the sand of an Albuquerque playground was under way on Saturday as investigators resumed their search for the boy's parents or guardian.

Police renewed their call for the public's help in finding out how the 3- to 5-year-old boy ended up buried in northeast Albuquerque's Alvarado Park. A mother at the playground with her children spotted a shoe sticking out of the sand and made the grim discovery on Friday afternoon.

"No one has stepped forward as parent, guardian or caretaker or any other relationship with this child," Albuquerque police spokesman John Walsh said on Saturday. "Anybody who has seen or heard of any, anything, involving a child in that area, we want them to call us."

Albuquerque Police Chief Ray Schultz said during a news conference late Friday that police have had no reports of missing children but believe he may be from the neighborhood.

The autopsy at the New Mexico Office of the Medical Investigator began at 9 a.m. Saturday, Walsh said, and will determine the cause and manner of the child's death.

The boy was wearing a red shirt with the image of a four-wheel drive truck on the front, black nylon pants with red stripes and black shoes. Police showed a photograph of the boy's clothing during the news conference in hopes that someone might recognize it.

A team of about 50 investigators canvassed the area around the park until early Saturday and resumed the effort after daybreak, Walsh said.

Forensic experts who exhumed the body told police that the boy could not have been dead longer than 48 hours, Walsh said.

Schultz said the case was unique because his department has not had any reports of missing children in the 24 hours before the body's discovery. He asked that anyone who had been to the park in the last couple of days to call police.

"This is one of those cases where I think every minute counts," Schultz said late Friday.

Neighbors said they were shaken by the discovery.

"I run in this park every day. I've lived here for 17 years, it's very upsetting," neighbor Marlisa Gomez told Albuquerque television station KOAT.