A powerful 7.1-magnitude earthquake struck in the southern Indian Ocean Saturday, but there was a low likelihood of casualties and damage, US seismologists said.

The shallow tremor struck at 6:24 am (22:24 GMT Monday), some 1,020 km (634 miles) east-northeast of Heard Island and McDonald Islands, the US Geological Survey said.

The epicentre was at the Southeast Indian ridge, a tectonic plate boundary located along the seafloor of the southern Indian Ocean.