Spokesman Morgan Lyons said, "They just needed oxygen, some fresh air."
He said the cause of the smoke wasn't known right away.
Three people were treated at the scene besides those who went to the hospital. Other passengers were picked up by a shuttle bus.
The outage shut down the northbound track of a tunnel under Central Expressway. DART was alternating northbound and southbound trains on the southbound track.
Lyons said they hoped to get both tracks open shortly.