The earthquake, measuring 7.3 on the Richter scale, hit the country at around 8:00 GMT. Most of the casualties were injured when buildings collapsed.
The number of casualties is expected to rise as the relief operation is still underway.
A spokesman for the country's meteorological agency told RIA Novosti the powerful undersea tremor was located 40 kilometers (25 miles) northwest of the town of Sinabang in the Aceh province.
Indonesia is often hit by earthquakes and volcano eruptions that trigger deadly tsunamis due to its location in the area of the so-called Ring of Fire, where movement and collision of crustal plates result in about 90% of the world's earthquakes.
In December 2004, a magnitude-9 earthquake with an epicenter off the west coast of Sumatra lead to a tsunami killing over 230,000 people in a dozen countries, most of them in Indonesia.
