By Rosalba O'Brien
SANTIAGO (Reuters) - An earthquake shook buildings and woke people in the Chilean capital Santiago before dawn on Wednesday, though there were no initial reports of damage or casualties.
The tremor, with a magnitude of around 5.5, struck 33km (21 miles) north of the city, the U.S. Geological Survey said.
Residents said they felt a strong shock at around 3.15 a.m. (0715 GMT). "Lots of shaking! Slight at first, one big shake, then continued for about 30 seconds," wrote one on the European-Mediterranean Seismological Centre's website.
"Woke me up, lots of shaking. Set off car alarms," wrote another.
Chile's emergency service Onemi said it received no reports of damage to services or infrastructure and the Chilean navy said it was not expecting a tsunami.
Chile, located on one of the "Pacific Ring of Fire" fault lines, has a long history of large quakes, including the largest recorded in history, a 9.5-magnitude quake in 1960.
The long, slender country runs along the border of two tectonic plates, with the Nazca Plate beneath the South Pacific Ocean pushing into the South America Plate, a phenomenon that also formed the Andes Mountains.
(Reporting by Rosalba O'Brien; Editing by Andrew Heavens and John Stonestreet)