A boy was killed and at least 15 others, including two Japanese nationals, were injured when a loaded bus plunged into a gorge in Manipur's Kangpokpi district on Tuesday, police said.The incident took place around 10.30 a.m. on National Highway-2, which links Manipur and Nagaland with other northeastern states.The boy -- N. Momocha -- was killed on the spot. Others were rescued from the 50-metre-deep gorge by police, medical staff and local youth.Police said investigations are underway to ascertain the cause of the accident.