The jailer says Daniel Patterson, Jr., 36, was being transferred from Clark County Detention Center to the Estill County Jail when he got away.
The police vehicle pulled near the jail, and when Patterson got out, he ran off, said the jailer.
Both Estill County police and Kentucky State Police are currently looking for the escapee.
The jailer adds Patterson is considered dangerous.
The escaped inmate was in custody for Robbery 1st, stemming from an armed robbery of a Cash Express in Clark County in June.
Patterson was due in Estill County court Wednesday for unrelated charges.