Jamie Lynn Spears' daughter, Maddie, 8, is reportedly in critical condition after an ATV accident Sunday.

According to a report by TMZ, the girl was underwater for several minutes after an ATV she was riding flipped over.

Maddie is the niece of pop superstar Britney Spears, whose sister, Jamie Lynn, made headlines in 2007 after announcing her pregnancy.

She was just 16 and engaged to Casey Aldridge, the father of her child. She's now married to Jamie Watson.

Photos | Jamie Lynn Spears and her daughter Maddie

Maddie's grandfather, Jamie Spears, spoke to E! News Sunday, urging the public to keep his granddaughter in their prayers.

"All I can say is pray for our baby Maddie," he says.

Sources in the Kentwood, La., area say she was riding a Polaris ATV while on a hunting expedition. According to reports, Jamie Lynn was not with her daughter at the time of the accident.

Maddie was airlifted to a nearby hospital.

Stay updated on this and other stories by downloading the FREE 11Alive News app now in the iTunes store or on Google Play.