Indonesian authorities say the death toll has risen to 21 from a series of strong earthquakes and aftershocks that have hit the western island of Sumatra this week.

Authorities announced the new death toll Saturday, as rescue workers tended to quake survivors. The health ministry now says at least 88 people have been injured.

Seismologists say Indonesia has been hit by at least 40 big aftershocks after an initial eight-point-four magnitude earthquake struck Wednesday.

Thousands of people are still sleeping outdoors for fear of falling debris. The quakes damaged hundreds of houses, leaving many people homeless.

Despite the destruction, a U.N. assessment team says there is no need for a major international relief effort. The team visited Bengkulu, an area near the epicenter of the quake on Thursday.

The Indonesian archipelago is prone to seismic activity because of its location on an arc of volcanos and fault lines circling the Pacific Basin.

In December 2004, a tsunami triggered by an underwater earthquake killed an estimated 230,000 people near Indian Ocean coastlines, including more than 160,000 people in Indonesia's Aceh province.

Some information for this report was provided by AFP  and Reuters.