SWA 3299 B737 lost an engine almost immediately after starting a takeoff roll. Sounds like a significant engine failure. Abort was succesful and airplane was able to taxi clear of the runway. Passengers were deplaned via airstairs and bused back to the terminal. No injuries. 144 pax + 5 crew aboard. Chicago FD units did report light smoke still coming from the engine after shutdown, but no visible fire. Runway 4R remained closed as ground personnel reported engine debris scattered down the runway. No abort call or comms from SWA3299; however, the SWA plane second in line saw the engine failure and called it out and tower contacted emergency crews before the plane had even stopped. They were enroute from quarters before 3329 even cleared the runway, so good job by the tower on being observant and quick in contacting the FD.
Plane cleared 4R at Kilo, and stopped on Kilo, between Delta and Yankee... only about 1,000' from where he started the takeoff roll. (MDW diagram attached)
Video from aboard of the moment the engine failed. You can hear the failure and immediate abort (about halfway in this new story, embedded in the tweet posted):
http://wgntv.com/2015/07/09/southwest-plane-aborts-takeoff-at-midway-due-to-engine-fire/Attached audio contains ground comms and tower comms, edited for time and most non-related communications.