Female substitute teacher goes on the run after she was accused of having sex with boy, 17, in an empty classroom

A teacher is on the run after being charged with allegedly having sex with a student in a middle school classroom.

Caitlin Thao, 24, was a substitute teacher at St Paul City School in Minnesota until earlier this year, where she encountered the teenager.

The school sent a letter to parents on Friday explaining the alleged illicit sex was with a 17-year-old boy after school hours in an empty classroom.

Thao appeared to have gone into hiding as a nationwide warrant was issued for her arrest by the Ramsey County District Court last week.

The teen told police on March 13 that he had sex with Thao in the classroom where she taught about six weeks earlier.

She invited him to her home but he declined, court documents alleged.

Thao resigned in late February just weeks later, and allegedly told a social worker at the Regions Hospital mental health unit where she was being treated.

Thao was charged with third-degree criminal sexual conduct and faces up to 15 years in prison and a fine of up to $30,000.