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Massive search: Isabel Mercedes Celis, 6, vanishes in Tucson, Ariz.

A massive search for a 6-year-old Tucson, Ariz., girl who vanished Friday night resumed Sunday morning.

Scores of police, FBI agents and deputy U.S. marshals combed the city’s east side for first-grader Isabel Mercedes Celis. Officials tried to determine if the girl was kidnapped or just wandered off.

Isabel’s parents last saw her in bed at 11 p.m. Friday, and they discovered her missing when they woke up around 8 a.m. Saturday, Tucson police spokeswoman Sgt. Maria Hawke said.

Police using dogs and a helicopter were still out late Saturday night, police communications operator Patrick Olea said.

Friends of the family distributed fliers with a photo of Isabel, NBC station KVOA in Tucson reported.

"We're really surprised or shocked that anything like this could happen to our family," the girl's uncle, Justin Mastromarino, told KVOA.

Hawke said investigators were looking into all potential scenarios, including the possibility that Isabel got up and wandered out of the home she shares with her parents and two brothers or that she was kidnapped.

Investigators also were examining every door and window of the house for signs of a break-in, Hawke said.

Both parents live in the home, so police had no indication a child custody dispute was involved but weren't completely ruling it out.

"We don't want to be caught behind the ball by not exploring that possibility," Hawke said Saturday afternoon.

The working-class neighborhood of single-family homes is sandwiched between a large shopping mall to the east and businesses and a Catholic school to the west.

Isabel is described as just under 4 feet tall and weighing 44 pounds, with brown hair and hazel eyes. She is missing her two front teeth.

This article includes reporting by The Associated Press.

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