An eight-year-old Missouri girl has died after suddenly becoming "ill and then unresponsive" during a SkyWest Airlines regional flight heading to Chicago, officials say. 

The Peoria County Coroner's Office says Sydney Weston of Carl Junction was traveling with her family on vacation when the incident unfolded Thursday morning. Skywest Flight 5121, which was headed from Joplin to Chicago, ended up making an emergency landing at Peoria International Airport around 7 a.m. local time. 

"Her family immediately notified the flight personnel of her condition, and they began rapidly rendering aid. Upon landing in Peoria, she was not breathing and had no pulse," the coroner’s office said in a statement. 

It added that "despite aggressive resuscitative efforts," Weston was pronounced dead at a local hospital about an hour later. An autopsy has been scheduled for Friday. 

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"SkyWest Flight 5121, operating as United Express from Joplin, MO to Chicago O’Hare diverted to Peoria, IL Thursday morning and was met by paramedics to attend to a passenger in medical distress," the airline told FOX Business in a statement. "We appreciate the efforts of our crewmembers who responded quickly to assist and the medical personnel who met the aircraft." 

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The Peoria County Sheriff's Office said, "When the plane landed, Deputies, AMT Personnel, and Air National Guard Fire personnel immediately received the 8-year-old female child and began life-saving measures." 

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"Please keep the child's family and everyone who was involved in this traumatic experience in your thoughts and prayers," it also said.