A former US Olympics gymnastics coach has killed himself hours after he was charged with sexual assault and human trafficking, officials say.

The office of Michigan Attorney General Dana Nessel confirmed the death of John Geddert on Thursday afternoon.

In the morning, Ms Nessel had outlined 24 felony charges facing Geddert.

Geddert was head of the women's gymnastics team in 2012 and worked closely with team doctor Larry Nassar who abused hundreds of athletes.

Nassar was sentenced to up to 300 years in jail in 2018 for abusing more than 250 girls.

Geddert, 63, had owned the training facility in Michigan where Nassar had served as the gym's doctor.

He was expected to turn himself in on Thursday afternoon but did not appear, the attorney general's office said.

"My office has been notified that the body of John Geddert was found late this afternoon after taking his own life," Ms Nessel later said in a statement.

"This is a tragic end to a tragic story for everyone involved."

Earlier, she had announced 24 separate charges against Geddert that "focus around multiple acts of verbal, physical and sexual abuse perpetrated by the defendant against multiple young women".

Two of the counts involved the alleged sexual assault of a girl between the age of 13 and 16.

Human trafficking charges related to his alleged use of "force, fraud and coercion against the young athletes... for financial benefit to him", Ms Nessel said, adding that it put the victims in harm's way.