Police have said a car which crashed in Enniskillen in the early hours of Saturday had failed to stop for police shortly before it hit a roundabout.
Five people were taken to hospital just before 02:00 BST after the accident at the Johnston Bridge roundabout.
One of them, a 23-year-old man, is said to be in a critical condition.
A sixth person, an 18-year-old man, was arrested but has since been released on bail pending further inquiries.
A number of roads in the area remain closed.
PSNI Insp Rod Flood said: "It is believed that six people were inside the car at the time of the incident.
"Two females, aged 42 and 22, and two males, aged 28 and 27, have been taken to a nearby hospital for treatment to injuries that are not believed to be life-threatening.
"One male, aged 23, has been taken to a nearby hospital with serious head injuries. His condition is described as critical."
BBC News NI reporter Julian Fowler visited the scene of the crash.
"The blue Ford Focus was travelling down the Cornagrade Road when it appears to have mounted the pavement and collided with a metal railing," he said.
"It then travelled across a traffic island before stopping in the middle of the roundabout."
Police have appealed for anyone with information to contact them.
The Johnston Bridge roundabout at the junction with the Cornagrade Road, Queen Elizabeth Road, Queen Street and Halls Lane remain closed to traffic.