(CNN) -- Eighteen tourists taking a hot air balloon ride in southern Egypt were killed Tuesday when the balloon exploded and plummeted to the ground, authorities said.
It was the deadliest hot air balloon accident in the world in at least 20 years.
Twenty-one people were in the balloon when it dropped about 300 meters (almost 1,000 feet) in the city of Luxor, the Egyptian interior ministry said.
Three people are hospitalized, and four remain missing, state-run EgyNews reported.
Earlier, the agency said 19 tourists had been killed but later revised that number.
A gas explosion caused the crash, EgyNews said.
Balloon rides offering panoramic aerial views of the Nile River and the ancient temples of Karnak and Hatshepsut are a popular tourist attraction in Luxor, about nine hours' drive southeast of Cairo.
Passengers in the balloon included 19 foreign tourists: nine from Hong Kong, four from Japan, three from Britain, two from France and one from Hungary, officials said.
An Egyptian pilot and another Egyptian were also on board, Luxor province spokesman Badawi al-Masri said.
The last hot air balloon accident in Luxor occurred in 2009, when 16 foreign tourists were injured after a balloon struck a cell phone transmission tower.
Unti Tuesday's incident, the deadliest accident in recent memory took place in 1989, when 13 people were killed when two hot air balloons collided in Australia.
Egyptian government spokesman Alaa Hadidi announced the Cabinet will form a committee from the Ministry of Civil Aviation to investigate the cause of the accident, EgyNews said.
CNN's Housam Ahmed and journalist Adam Makary in Cairo contributed to this report.
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