A major earthquake of 7.8 magnitude struck off the coast of Aceh on the Indonesian island of Sumatra on Wednesday, but there were no immediate reports of casualties.The quake, which struck around (2215 GMT), was centered 200 km west-northwest of the coastal town of Sibolga and was at a depth of 31 km, the US Geological Survey said. The epicentre was around 215 km from Medan, the largest city on Sumatra. The witness said there were at least three aftershocks. The Hawaii-based Pacific Tsunami Warning Center initially warned the quake could generate a local tsunami, but later cancelled its tsunami watch, saying: Sea level readings indicate that a significant tsunami was not generated. An official from Indonesia's meteorology agency said a tiny tsunami of only 3 cm (1 inch) had been detected at Sinabang and lifted its own tsunami warning.