An earthquake measuring 6.5 on the Richter scale rocked the western part of Sumatra island on Thursday, but there were no immediate reports of damage, the geophysics agency said.
The quake occurred at 5:56 am (2356 GMT Wednesday) with the epicentre 79 kilometres south-west of Pesisir Selatan district, at a depth of 72 kilometres, according to the Meteorology, Geophysics and Climatology Agency.
A resident in Bukittinggi, West Sumatra province, said the tremor was felt strongly there.
"Residents ran out of their homes and stayed outside for some time because they were afraid of an aftershock," the man whose name was given only as Epi was quoted as saying by Antara news agency. Many Indonesians go by only one name.