Bangkok - A Thai military air show for children was marred by tragedy on Saturday when a fighter jet plunged from the sky and burst into flames, killing the pilot.Families were gathered at the airport in the southern city of Hat Yai to watch the show put on for Thailand's annual Children's Day.Footage of the accident captured shrieks from a startled crowd as the jet took a nosedive and crashed near the airport's runway, releasing fiery plumes of smoke. Defence ministry spokesperson Major General Kongcheep Tantravanich said: "One pilot was killed in the accident this morning."The cause of the crash was under investigation, he added. No one else was injured in the incident, according to an airport official, as the audience was gathered a considerable distance away from the crash site. A junta spokesperson said the 35-year-old pilot was flying a Swedish-made JAS 39 Gripen jet. Thailand's national Children's Day is celebrated annually on the second Saturday of January. The holiday sees military bases around the country open up their gates to let youngsters handle guns and climb over tanks and warships.Many zoos and museums also allow children in for free.