There were no immediate reports of casualties, but residents ran screaming out of buildings.
The new earthquake - measuring 6.2 on the Richter scale - shook the Bengkulu region, where more than 100 people died in the original tremor.
There were no immediate reports of casualties, but residents ran screaming out of buildings.
The new quake was deeper and centred slightly south of Sunday's 7.9-magnitude tremor.
But there was better news from Enggano island, reached for the first time by relief workers since the earlier earthquake.
Few casualties were reported, though many houses collapsed and food and shelter are urgently needed.
The second earthquake struck at 0645 (2345 GMT Wednesday), in the Indian Ocean about 200km (125 miles) south-east of Bengkulu. France's Strasbourg observatory measured it at 6.7.
"The quake was felt quite strongly early this morning, and everyone ran out of the buildings. Even those in tents ran out of
them in panic," a photographer for AFP news agency said.
Rescue operations in Sumatra are continuing, amid growing criticism of the slowness of Indonesia's own response.
The parliamentary speaker, Amien Rais, who has been touring the affected area, said he was ashamed that foreign governments and aid agencies had reacted much more promptly than his own government.
Soon after the latest tremor, about 100 homeless people were reported to have blocked a key road to protest at the slow government response. About 30 police struggled to defuse tensions.
Asian quakes
Hospital officials and local media say around 120 people were killed and some 1,300 injured in Sunday's quake, one of the biggest to hit Indonesia in recent years.
Thousands of homes and other buildings were destroyed.
Foreign aid has been arriving in the region, but relief efforts have been hampered by heavy rains and flooding.
Earthquakes have recently rocked other parts of the region.
Japan had three fairly strong earthquakes this week and China and Myanmar each had two.
On Wednesday, a tremor measuring 5.8 on the Richter scale struck central Japan while on Thursday, a quake measuring 6.3 hit the areas bordering Myanmar and China.
Experts have said that the series of quakes could have sprung from Sunday's earthquake in Bengkulu causing a shift in the large tectonic plates in Asia's seas.