(Adds no initial reports of damage, quotes)
LIMA, July 18 (Reuters) - An earthquake with a magnitude of 6.4 struck off the coast of Peru on Monday, the U.S. Geological Survey said, though Perus civil defense institute Indeci said there was no risk of a tsunami and no immediate damage.
The quake, which was initially measured by the Pacific Tsunami Warning Center at 6.3, was 44 km (27 miles) deep and centred 194 km (120 miles) southwest of Puquio, Peru, the USGS said.
The quake was felt in Peru's second largest city of Arequipa and in northern Chile, local media reported.
Mining company Southern Copper had no reports of damage at its two mines in southern Peru, company spokesman Guillermo Vildalón said.
Arequipa region's President Yamila Osorio said on Twitter authorities were monitoring rocks that had fallen on local roads.
Though the earthquake appeared not to have caused injuries, residents of small towns like Caravelí were startled and ran out of their homes, Caraveli mayor Santiago Neyra told local radio station RPP.
Earlier on Monday a magnitude 7.8 magnitude earthquake off Russia's Kamchatka Peninsula triggered a tsunami warning but the threat soon passed, the U.S. Geological Survey and U.S. Pacific Tsunami Center said. (Reporting By Marco Aquino; Additional reporting by Eric Meijer; Writing by Caroline Stauffer; Editing by Michael Perry and Kim Coghill)