A major earthquake measuring magnitude 7.3 shook a remote area of the South Atlantic today but was unlikely to have caused a tsunami, the US Geological Survey said.
USGS geophysicist Bruce Presgrave said the quake's horizontal motion "makes it unlikely for a tsunami".
"Also, the water depth there is rather deep and also at magnitude 7.3 that's usually too small to produce an ocean-wide tsunami even if the other conditions were right.
"So basically, this is a big earthquake a long way from anywhere," Mr Presgrave said.
Since the tsunami that devastated parts of southeast Asia in December 2004, the world has been on higher alert for the potential of undersea quakes to trigger another giant wave.
The USGS described it as a "major quake" that occurred at a depth of 6 miles. It occurred at 06.10 am about 215 miles southeast of Bristol Island, South Sandwich Islands, a British territory, and about 2,450 miles south-southeast of Buenos Aires.
The quake was "in a remote area and no damage or casualties are expected", the USGS said on its Web site.
Matti Tarvainen, senior scientist at Finland's Institute of Seismology, which earlier expressed concern about a possible tsunami, said: "It is very unlikely that this will cause a tsunami.
"As we have gained more information ... we have found that the motion is such that there is hardly any vertical movement."
The Finnish institute gave coordinates for the quake of 61 degrees south and 22 degrees west.