However dozens of people could be buried under the remains of hundreds of collapsed buildings on the island of Nias, close to the quake's epicenter.
"Hundreds of buildings have been damaged or have collapsed. People who were standing fell over. We're not sure about casualties, but there may be dozens of people buried in the rubble," said Agus Mendrofa, deputy district head on Nias island which was nearest to the epicenter of the quake.
The U.S. Geological Survey said the temblor had a magnitude of 8.7 and was an aftershock of the Dec. 26 quake that sent giant waves crashing into coastlines around the Indian Ocean's rim and killing more than 174,000 people in 11 countries.
The USGS had earlier said the earthquake had a magnitude of 8.2.
"It seems this earthquake did not trigger a tsunami," Prihar Yadi, a scientist with the Indonesia Geophysics Agency. "If it had, the tsunami would have hit the coastline of Sumatra by now. And if there's no tsunami on the coastline near the epicenter of the quake, there will not be one heading in the other direction."
A Thai expert also said the threat of a tsunami had probably passed. Smith Thammasaroj, a former chief of the country's meteorological department, told a local television station that it appeared that southern Thailand would be spared from any possible tsunami from the quake.
In Sri Lanka, the military said it had no sign of a tsunami yet but wanted to wait a bit longer before declaring that things were safe.
The quake cut electricity and sent people scurrying for high ground in Banda Aceh on Sumatra's northern tip, the area hardest hit by December's tsunami. The quake lasted for about two minutes, far longer than most of the daily aftershocks that have rocked Aceh since Dec. 26.
"People are still traumatized, still scared, they are running for higher ground," said Feri, a 24-year-old recovery volunteer who goes by one name.
Sirens blared along Sri Lanka's devastated east coast as the government warned seaside residents to evacuate immediately.
"The government has ordered coastal areas to move to higher ground. We are giving priorities to eastern coast," said Brig. Daya Ratnayake, the military spokesman.