The number of people left homeless after an earthquake struck western Indonesia has soared to nearly 84,000, leaving authorities struggling to care for the victims, an official said Tuesday.

The shallow quake last week killed more than 100 people and injured many more when it struck Aceh province, one of the areas worst affected by the devastating Indian Ocean tsunami in 2004.

Thousands of homes, businesses and mosques were levelled by the 6.5-magnitude quake, which struck at dawn as many in the predominantly Muslim region were preparing to pray.

Hospitals and field clinics were quickly overwhelmed by the injured, and kitchens and shelters swamped by people left with nothing.

As the scale of the disaster continues to unfold, the number of those displaced has nearly doubled to more than 83,800, said national disaster agency spokesman Sutopo Purwo Nugroho.

"People are afraid and worried about aftershocks, so feel more comfortable in the evacuation shelters," he said in a statement Tuesday.

"The problem with water supply at some of evacuation points is not good," he added, saying wells had been left dry since the quake.

Aid has begun reaching the worst-hit areas but there was still an urgent need for more food, clothing and sanitation products, the agency said.

Indonesian President Joko Widodo visited the province last week, pledging to rebuild the area's devastated communities.

The archipelago nation experiences frequent seismic and volcanic activity due to its position on the Pacific "Ring of Fire", where tectonic plates collide.

A huge undersea earthquake in 2004 triggered a tsunami that engulfed several countries around the Indian Ocean, killing more than 170,000 people in Indonesia alone, the vast majority in Aceh.

The province lies on the northern tip of Sumatra island, which is particularly prone to quakes.

In June, a 6.5-magnitude quake struck off the west of Sumatra, damaging scores of buildings and injuring eight people.