Craig Nelson Ross Jr, 47, is in custody over her disappearance, New York state governor Kathy Hochul told a news conference.

She disappeared while riding her bike on Saturday evening in Moreau Lake State Park, about 35 miles (60km) north of Albany.

When she didn't return 15 minutes later, her parents and nearby campers began to search the area.

Ms Hochul said officials identified a fingerprint on a ransom note that had been delivered to the family while the home was being monitored by police, from data gathered in 1999 after a drink-drive incident.

She added after the note was identified, police swooped in on the suspect's home, a camper van behind his mother's house, and Charlotte was found in a cupboard by officers, and does not appear to have been harmed.

"She knew she was being rescued. She knew that she was in safe hands," Ms Hochul said, adding the girl has been reunited with her family.

More than 100 personnel and 75 law enforcement officials were deployed in the search for the girl, which also included dogs, two drones, boats and six underwater rescue teams, Ms Hochul said earlier.

Earlier on Monday, police said 400 search and rescue personnel were looking for the nine-year-old, across a space measuring 46 miles.

Police set up checkpoints in the park, while stopping cars and checking vehicles as they drove through.

The park was closed while the search took place, with officials asking the public to stay away.

Police added the FBI was also helping in the case.

Charlotte's aunt, Jene Sena, told Sky's US partner network NBC News that her niece vanished in only minutes.

"She disappeared almost into thin air. I mean it was, minutes, minutes, between when she was last seen and when she wasn't there anymore," Sena said.