A powerful earthquake jolted the western Indonesian island of Sumatra, killing a 12-year-old boy and sending people streaming from their houses and hotels in panic.

Hundreds of patients from at least one hospital had to be evacuated, some in wheelchairs or with infusion drips still attached to their arms.

The U.S. Geological Survey said the 6.6-magnitude quake was centred 100 kilometres southwest of the city of Medan at a depth of 110 kilometres.

It was too far inland, however, to generate a tsunami.

The temblor hit at about 1 a.m. local time Tuesday, rattling people from their sleep in towns and villages across the island's northern tip.

Maura Sakti, a mayor in Subulussalam, told the local station TVOne a 12-year-old boy had been killed.

He had no other details about injuries or damage.

'We saw our walls start to crack'

Residents in Singkil, nearer to the quake's epicentre, said some electricity poles were knocked down, crashing into homes and causing blackouts.

"My wife was screaming, my children crying," said Burhan Mardiansyah, 37. "We saw our walls start to crack and everything inside the house was falling."

"Thank God we're all safe."

Marni Aulia, a 32-year-old vendor in the town, said two hours after the quake people were still afraid to go back inside.

"We're worried about the aftershocks," she said.

Indonesia straddles a series of fault lines that make the vast island nation prone to volcanic and seismic activity.

A giant quake off the country on Dec. 26, 2004, triggered a tsunami in the Indian Ocean that killed 230,000 people, half of them in Indonesia's westernmost province of Aceh.