More than 100 people are searching for a 9-year-old girl who went missing while camping with friends and family members Saturday in upstate New York, the governor said.

Charlotte Sena was camping in Moreau Lake State Park with her family and went on a bike ride with close friends around dinner time Saturday evening, New York Gov. Kathy Hochul said in a news conference Sunday.

After biking a couple of loops together, "she just wanted to go around one more time by herself, be that big girl and do it by herself," the governor said.

When Charlotte didn't return roughly 15 minutes later, her parents "knew immediately something was up," and began calling her name. People from other campgrounds soon joined the search, Hochul said.

The girl was last seen around 6:15 p.m. ET riding her bike in one of the park's loops, Lt. Colonel Richard L. Mazzone, of the New York State Police, said in the news conference.

At about 6:45 p.m., her bike was found in the loop, Mazzone said.

Two minutes later, her mother called authorities to report her missing.

Charlotte was last seen wearing an orange tie-dyed Pokémon shirt, dark blue pants, black Crocs and a grey bike helmet, according to a description provided by the state police. She is White with blonde hair, about 4' 6'' tall, with green eyes, authorities said.

An AMBER alert was issued Sunday morning, Mazzone said.

"We took that step of issuing the AMBER alert because we felt, after (our) exhaustive search, when we couldn't find her here, it was quite possible that an abduction had taken place," he added.

For more than 18 hours, state authorities have been searching for the child and have deployed aviation and underwater rescue teams, blood hounds, drones and technology experts have also been called in to analyze "other forms of communications in the park at that time," the governor said.

Charlotte is the niece of a member of the Schenectady Fire Department, which is also helping with the search, Hochul added.

"We are leaving no stone, no branch, no table, no cabin unturned, untouched, unexamined in our search to find Charlotte," she said. "If you know anything, if you've seen anything, if you hear anything, please contact 911 to tell us what you know."

Charlotte is a fourth grader who was recently elected to be a class officer for student council, Hochul said.

"Hearts are broken here today in New York. Hopefully there will be a reunion, hopefully there will be a family that has been traumatized but is reunited," she said. "That is our prayer and our hope."

Moreau Lake State Park, in Saratoga County, is more than 4,600 acres and "lies amid hardwood forests, pine stands and rocky ridges," according to the Department of Environmental Conservation. It's roughly 45 miles north of Albany.

The park said in a Facebook post it is closed until further notice.