SANTIAGO (REUTERS) - An earthquake of magnitude 6.8 struck off Chile's coast on Thursday (Aug 1), the US Geological Survey (USGS) said, but local authorities said there was no immediate report of any damage.

The quake, initially reported as a magnitude 6.5, was centred 140km south-west of the coastal city of Valparaiso in central Chile, the USGS said.

The quake was very shallow below the seabed.

No injuries, damage or disruptions to basic services had been reported, Chile's National Emergency Office said in a statement, adding that government agencies were monitoring the situation.

The navy's information service also concluded that the earthquake did not pose a tsunami risk, the statement said.

Chile, located on the Pacific "Ring of Fire," has a long history of deadly quakes, including an 8.8 magnitude quake in 2010 off the south-central coast that triggered a tsunami that devastated coastal towns.