WASHINGTON (AFP) - A powerful 6.9 magnitude earthquake struck in the far south Atlantic ocean in the inhospitable South Sandwich Islands region, the United States Geological Survey (USGS) said on Sunday.

The USGS, which monitors quakes worldwide initially said the quake was of magnitude 7.1, but later revised its strength downwards. It also slightly revised the epicentre's location.

The quake, which struck at 7.52am, had an epicentre 154km north-west of the uninhabited Visokoi Island, and 1,975km east-south-east of Stanley, the main city on the Falkland Islands, the USGS reported. The epicentre was at a depth of 16.5km.

The Hawaii-based Pacific Tsunami Warning Centre issued a bulletin stating that, based on historical data, "a destructive widespread tsunami threat does not exist". The quake occurred near the boundary between the Antarctic tectonic plate and the Scotia Sea plate, two plates that slide past one another horizontally.

Earthquakes in the Pacific Rim area are more likely to trigger tsunamis because they are usually subduction quakes, when one tectonic plate moves under another and triggers a vertical movement in the seafloor.

The South Georgia and the South Sandwich Islands is a British overseas territory. There is no native population to the islands, but there are scientific research outposts. Argentina claims the archipelago as well as the Falkland Islands to the west.