The quake originated offshore from Sumatra's northeastern tip, authorities said, prompting people to flee outdoors in a region that frequently experiences devastating tremors.

"I was at home when it happened... the shaking was really strong," 50-year-old Ahmadi, who, like many Indonesians, uses only one name, told AFP by telephone from the small coastal town of Sinabang in the northernmost Aceh province.

"I panicked. We fled the house, but because the jolt was pretty short, things went back to normal," he added, adding he could see "families running around here on the street".

Rahmat Triyono, head of Indonesia's BMKG earthquake and tsunami centre, said people on Simeulue island and east-coast areas of Aceh would have experienced a strong tremor, with windows and doors rattling, walls creaking and possibly some broken glassware.

But he said there was no tsunami risk.

Weaker shaking was also felt in Sumatra's northeast.

The vast archipelago nation experiences frequent earthquakes due to its location in the Pacific "Ring of Fire" -- an arc of intense seismic activity where tectonic plates collide that stretches from Japan through Southeast Asia and across the Pacific basin.

In 2004, a magnitude-9.1 quake struck Aceh province, causing a tsunami and killing more than 170,000 people in Indonesia.