Where are Indonesia and Sumatra?
Indonesia is situated in southeast Asia. The nation is made up of more than 14,000 volcanic islands between Asia and Australia and has a population estimated at 255 million people.
Sumatra, part of the Sunda Islands, is an island located in western Indonesia. Measuring just over 473,000 km2, Sumatra is the sixth largest island in the world.
Where was the earthquake?
On Wednesday, a shallow earthquake struck the western coast of Sumatra, which according to the US Geological Survey measured a magnitude of 7.9. Its centre was detected about 10km under the ocean.
In 2004, a tsunami, triggered by a magnitude-9.1 earthquake which hit Indonesia on 26 December, killed 230,000 people across dozens of countries. Nearly 127,000 deaths were in Aceh, a territory which is located at the northern end of Sumatra.
Are there any tsunami alerts in place?
As the earthquake on Wednesday afternoon was shallow, officials in Indonesia warned that it could trigger a tsunami.
But a tsunami warning which had been issued for West Sumatra, Aceh, Lampung, North Sumatra and Bengkulu was later cancelled.
Irwan Prayitno, the governor of West Sumatra, told Kompas TV: "We continue to remind residents to be careful and be on standby, but at this point, the possibility of a tsunami is smaller as compared to much earlier... when the quake first occurred."
Although Australia's Bureau of Meteorology initially issued a warning from Cape Preston to Bremer Bay, it was later cancelled too. Marine warnings remain in place for Cocos Islands and Christmas Island, which are located south of Indonesia in the Indian Ocean.
The Australian Federal Police said: "Evacuations from communities are not required, but people are advised to get out of the water and move away from the immediate water's edge of beaches, harbours, marinas, coastal estuaries and rock platforms."