The quake sparked fears of another tsunami similar to the one that devastated the region on Dec. 26, killing an estimated 174,000. When seas failed to rise in the hours after the earthquake, worries of a possible tsunami faded. But at least 13 aftershocks with magnitudes between 5.0 and 6.1 have shaken the area.
While the tremor was two to four times less powerful than the 9.0 quake in December, it was still one of the eight largest earthquakes since 1990.
Many buildings in Nias island's main town of Gunung Sitoli were destroyed. While bodies were collected at a town mosque, relief workers treated the injured on a soccer field, according to the Reuter's news agency.
Nias, a remote island about 870 miles northwest of Jakarta, has a population of about 700,000. The island has become a popular resort in recent years, especially for surfers.
Vice President Jusuf Kalla told the el-Shinta radio station in Jakarta that the death toll could rise to 1,000-2,000.
Indonesia's president Susilo Bambang Yudhoyono sent condolences to the victims' families and postponed a trip to Australia to survey the damage in Nias.
He said the country was offered help from around the world. "We welcome and highly appreciate it," he said.
In Washington, U.S. officials said they would answer the call.
"We're applying what we've learned from the pervious earthquake so that we can be prepared to be responsive quickly and in a meaningful way," State Department spokesman Adam Ereli said Monday.
The aid effort may be hampered by the island's remoteness and the havoc caused by the temblor. The quake damaged the town's airstrip, allowing only small planes to land. The International Organization for Migration said it would send trucks with water, milk and other essentials to the Sumatran port town of Sibolga and the supplies would be ferried to Gunung Sitoli.
"Bodies are being pulled from the rubble as I speak," said Alessandra Boas, a member of Oxfam's assessment team. "The water system has failed completely and huge holes have been made in the roads."
Although the damage and deaths were centered on Nias, the quake sent shock waves through countries still recovering from December's devastation. Several Asian countries issued tsunami warnings, causing residents to panic and flee.
Warning sirens sounded in Sri Lanka and President Chandrika Kumaratunga urged people to evacuate.
"It was like reliving the same horror of three months ago," Fatheena Faleel, the mother of three, told the Associated Press.
Monday's earthquake was felt as far away as Thailand, Malaysia and Singapore.