A person is in custody after police say a child was left in a hot vehicle near a Portillo's restaurant on National Hot Dog Day.

The child, who authorities believe was about 5 years old, was found inside a vehicle just after 11:30 a.m. in the 1000 block of Clinton, police said.

Officers in a marked squad car said someone flagged them down after seeing the child left alone in the vehicle.

Authorities said the owner of the vehicle was located and the child was evaluated by Chicago Fire Department officials at the scene and said to be in good condition.

The owner of the vehicle was taken into custody and charges were pending, police said.

The Portillo's located at the corner of Taylor and Clinton Streets declined to comment on what happened.

One witness, who was in the drive-thru lane at the restaurant, said the child appeared to be in the car in the restaurant's parking lot for about 15 minutes. Police could not immediately confirm how long the child was in the car, however.

“It was an interesting scene. Everyone was pretty startled," said Jon Gusanders.

Gusanders said he heard from staff that a child was in a vehicle and that police were being called. He watched the scene unfold as police and paramedics arrived.

"Kudos to [the staff] for not only noticing that but immediately calling police," he told NBC 5.

Gusanders added that he felt it was shocking someone would leave their child in the car on a hot day, especially at a restaurant that has a drive-thru.

"None of it makes sense," he said.

Temperatures Wednesday reached into the upper-80s in the city, with heat index levels in the low-90s.

Portillo's was offering Chicago-style hot dogs for $1 with purchase of an entree in honor of National Hot Dog Day. The deal began at 10:30 a.m. but was only available for dine-in and drive-thru customers.