The St. Johns County Sheriff's Office said it was responding Saturday night to a "despondent individual" on U.S. 1 near State Road 312.
SJSO said there is no threat to public safety and it is working to get the man the help he needs.
SJSO is asking people to avoid the area if possible.
Several people called the Action News Jax newsroom saying they saw a man on the roof of the Wendy's restaurant in that area.
As of late Saturday night, the man had been on the roof of the building for several hours, according to witnesses.