Pilots of a Southwest Airlines flight were forced to abort landing at Chicago's Midway Airport after spotting another aircraft crossing the runway, in a terrifying near-miss caught on video.

       The Southwest Airlines Flight 2504, arriving from Omaha, Nebraska, was about to touch down at 8.50am CST on Tuesday when the crew had to quickly pull up and climb back to 3,000 feet to avoid a collision.

       The aircraft had briefly touched the runway before suddenly ascending again.

       In a terrifying moment captured in radio transmissions, the Southwest pilot said: “Going around, Southwest.”

       Seconds later, the pilot could be heard questioning air traffic control with a chilling three words: “How’d that happen?”

       READ MORE: Moment plane nearly crashes into jet on runway as pilot makes incredible move

       According to the Federal Aviation Administration (FAA), the second aircraft - a Flexjet Bombardier Challenger 3500 private jet - entered the runway without authorisation.

       The private jet was set to depart for Knoxville, Tennessee, when it unexpectedly crossed into the Southwest plane’s landing path.

       The FAA and the National Transportation Safety Board (NTSB) have launched investigations into the incident.

       A spokesperson for Southwest Airlines confirmed that the flight crew followed safety procedures and landed without incident after the go-around.

       “Nothing is more important to Southwest than the safety of our customers and employees,” the airline said in a statement.

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       Flexjet, the private jet operator, acknowledged the incident, saying: "Flexjet adheres to the highest safety standards, and we are conducting a thorough investigation.

       “Any action to rectify and ensure the highest safety standards will be taken."

       The dramatic moment comes amid a string of near-miss incidents in the US aviation industry.

       Just days earlier, a midair collision at Arizona’s Marana Regional Airport resulted in two fatalities when a Cessna 172S and a Lancair 360 MK II crashed while approaching the runway.

       In December, a Delta plane narrowly avoided a collision with a private jet at Los Angeles International Airport, carrying the Gonzaga University men’s basketball team.