JAKARTA, Indonesia – A 7.7 earthquake shook Indonesia's northwest island of Sumatra early Wednesday, prompting a brief tsunami warning and sending residents rushing for higher ground. There were scattered reports of injuries, but only minor damage was immediately reported.

The quake struck at 5:15 a.m. (2215 GMT) and was centered 125 miles northwest of the coastal town of Sibolga in Sumatra at a depth of 19 miles (31 kilometers), the US Geological Survey said. It had earlier said the quake measured 7.8.

Indonesia's Meteorology and Geophysics Agency and the Pacific Tsunami Warning Center in Honolulu issued tsunami warnings following the quake, but lifted them two hours later.

Six people were hospitalized in Sinabang on Simeulue island with injuries sustained when their homes collapsed, a nurse at the local hospital said. One man was in critical condition.

Fauzi, a seismologist at the meteorology agency, said the quake would have “at least caused cracks in many buildings and houses, especially in areas closest to the epicenter.”

“That's why we are still trying to get data of damage in some remote areas that remain difficult to reach due to lack of communication and blackout,” said Fauzi, who goes by only one name.

Local network Metro TV reported that a dormitory for nurses partially collapsed in Aceh's Singkil district and one woman suffered minor injuries in the rush to get out of the building.

At least five strong aftershocks measuring up to 5.2 were recorded, the meteorology agency said.

The quake, which struck as people in the region were preparing for morning prayers, caused panic in North Sumatra's capital of Medan, about 135 miles (215 kilometers) from the epicenter, and other cities in the region. Electricity was cut in Medan, Banda Aceh – the provincial capital of Aceh – and other areas.

People in several cities along the southeastern coast of Sumatra as well as Sinabang on Simeulue island and Gunung Sitoli on nearby Nias island poured into the streets and rushed to higher ground after the quake.

Many fled their homes or piled onto motorcycles to head inland in fear of destructive waves, but a tsunami warning issued by the Indonesian government was lifted about two hours later.

“I was sleeping when the quake struck. I woke up my wife and my two kids and all of us hopped onto the motorcycle
and headed to higher ground,” said Agus, 30, who lost his mother and two siblings in the 2004 disaster.

“I saw my neighbours were all panicking too. It brought back bad memories of the 2004 tsunami.... I don't want to go back yet because my house is too near the sea.”

“Rumors about a tsunami panicked villagers living near the beach,” said Eddy Effendi, a resident on Nias island. “They ran away on motorbikes and cars or by climbing the hills. There was panic and chaos everywhere, but I don't see serious damage or injuries in my village.”

Residents in Sibolga said the shaking lasted more than a minute and utility poles in the area were knocked down.

The quake was felt as far away as the outskirts of Malaysia's Kuala Lumpur, about 320 miles (515 kilometers) away. There were no reports of damage there.

A 2004 tsunami triggered by a magnitude-9.2 earthquake in the same part of Indonesia killed 230,000 people in a dozen countries on the Indian Ocean basin.

Electricity poles swayed
The Hawaii-based Pacific Tsunami Warning Center initially warned the quake could generate a local tsunami, but later cancelled its tsunami watch, saying: “Sea level readings indicate that a significant tsunami was not generated.”

An official from Indonesia's meteorology agency said a tiny tsunami of only 3 cm (1 inch) had been detected at Sinabang and lifted its own tsunami warning.

A Metro TV reporter in the Sibolga area of North Sumatra said that he fell off his motorbike when the quake struck and the force left electricity poles swaying for minutes afterwards.

Tremors from the quake were felt in Dumai, in Sumatra's Riau province about 1,100 km from the epicentre, Indonesia's Antara news agency reported.

Hamid Sarong, a resident of Aceh's provincial capital Banda Aceh, which was devastated by a tsunami in 2004, said that the quake was felt while people in the staunchly Muslim province were at dawn prayers, although there was no panic.

Sumatra lies along the Pacific “Ring of Fire”, one of the world's most active seismic faultlines, and is frequently hit by earthquakes.

In December 2004, a magnitude 9.15 quake off Aceh triggered an Indian Ocean tsunami that killed about 226,000 people in Indonesia, Sri Lanka, India, Thailand, and nine other countries.

A 7.6 magnitude quake struck last September off the city of Padang, southeast of Wednesday's epicenter, killing more than 1,000 people. (AP, Reuters, and AFP)