Authorities say their estimate of up to 1,000 deaths there is based on damage to buildings rather than any body count. They say about 70 percent of the structures in the island's main city of Gunung Sitoli have collapsed or been seriously damaged.
Indonesian Information Minister Sofyan Djalil said emergency relief supplies must be delivered by military helicopters because of damage to the island's only airport.
"The airport in Gunung Sitoli still cannot be used for landing by airplanes because its control tower has collapsed and the runway is badly damaged," he said.
T.B. Silalahi is a special envoy sent to Nias by Indonesian President Susilo Bambang Yudhoyono. "The area itself is quite small," Silalahi said. "The population of Nias is only about 700,000 people. But I think there is still a need for foreign military help. And also, of course, aid efforts by any country for the area are most welcome."
Correspondents in the coastal areas where the quake was felt describe scenes of extraordinary panic. Tens of thousands of people were on the roads during the night trying to get to higher ground.
UN emergency relief coordinator Jan Egeland says that is because memories are still fresh of the tsunami that left 300,000 people dead or missing in December after a 9.0-magnitude quake in the same region.
"We see this as yet another example of panic spreading -- of deep concern in an already mentally scarred population," Egeland said. "It will cast shadows not only over our relief efforts, but very much also the reconstruction and rebuilding efforts."
Tens of thousands of people also spent a sleepless night on high ground along the coasts of India and Sri Lanka after tsunami warnings were issued there. By this morning, there was great relief that the tsunami never arrived on their shores.
But scientists warn residents to remain vigilant about powerful earthquakes in the future. They explain that there was, indeed, a tsunami as a result of yesterday's earthquake.
That wave was measured at 25 centimeters in the Cocos Islands in the southern Indian Ocean. December's catastrophic tsunami measured 32 centimeters in the Cocos Islands.
Tsunamis are magnified as they run up against continental shelves.
But experts say the fault line along the Sumatran coast directed this tsunami farther south across the Indian Ocean and toward Antarctica.
Meanwhile, in the other direction -- between the epicenter and the coast of Sumatra -- the shallow depth of the water weakened the severity of the wave from yesterday's quake.
"This looks like a fraternal twin of the December 26 earthquake," says Kerry Sieh, an expert at the U.S. Geological Survey in Pasadena, California. "It will probably not have as long a break. The rupture will probably not be as long as the 1,300 kilometers or 800 miles of the earthquake on December 26. But I would certainly say it is a fraternal twin. It's not a duplicate. It occurred a little bit further south. But it's the same kind of earthquake."
The latest earthquake appears to be increasing pressure on governments to establish a unified tsunami-warning system in the Indian Ocean.
The tsunami warning issued yesterday came from a Pacific station in the Hawaiian Islands.