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BOGOTA, Sept 9 (Reuters) - A strong 6.8-magnitude earthquake hit near the west coast of Colombia on Sunday night, the U.S. Geological Survey said, but local authorities said there were no immediate reports of serious damage.

Officials in coastal Narino province said they had no news of damaged buildings or injuries, but they were still contacting remote rural areas. Residents told local radio the shock knocked out electricity in some areas.

"For now, the checks conducted by operational units show no reports of any impact, but we will have to wait for the results of monitoring," said Luz Amanda Pulido, national director of Colombia's disaster prevention office.

An aftershock of 3.8 magnitude rattled the area shortly after the initial quake, Colombian authorities said.

Vindell Hsu, a geophysicist with the Pacific Tsunami Warning Center in Hawaii, told Reuters by telephone: "At this moment we are not giving any warning to any area. There might be small waves locally."

The quake occurred at a depth of 6.2 miles (10 km) and its epicenter was 95 miles (155 km) southwest of the Colombian port city of Buenaventura, the USGS said.

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