Ten people died from the massive earthquake that struck off Indonesia's Sumatra island earlier this week, official sources said Friday, revising an earlier toll of five dead.

Wednesday's 8.6-magnitude quake triggered an Indian Ocean-wide tsunami alert which caused little damage and few casualties.

"According to the latest data 10 people died," National Mitigation Agency spokesman Sutopo Purwo Nugroho said.

"Eight of the deaths were from heart attacks and the cause of the other two deaths is unknown," he said, adding that all of the casualties were in Aceh province, where 170,000 people died in a 2004 tsunami.

Nugroho said that most of the dead were aged between 60 and 70, and were believed to have died of shock.

He added that four people were seriously injured and hospitalised, including a child who fell from a tree. Eight others were lightly injured, he said.

Indonesia reported minimal damage from the quake, and the aftershocks that rumbled all night.

Damage was minimal because the epicentre was much farther offshore than 2004, according to the Meteorology and Geophysics Agency.

Minimal damage was caused this time round because government regulations ensured buildings have better resistance to quakes, according to the United Nations Development Programme (UNDP), and people were better prepared.

"The buildings in Aceh are now stronger because the government has set certain standards that oblige contractors to ensure anti-earthquake aspects are put in place," UNDP national project coordinator for Aceh Fahmi Yunus said.

Experts said an Indian Ocean-wide warning system -- that alerts people of a potential tsunami, through SMS messages, smartphones and social media -- helped spread the word across Indonesian Sumatra and other nations such as Thailand and India, prompting people to seek higher ground.