LISBON, PORTUGAL - A strong 6.0-magnitude earthquake struck Wednesday hundreds of kilometres off Portugal's Azores Islands in the Atlantic Ocean, US and Portuguese geologists said.

The US Geological Survey said that the quake struck 445 kilometres (277 miles) south of the islands at a depth of 10 km at 4:41 pm (1841 GMT), but it was not felt in the region.

The remote islands form a quake-prone Portuguese archipelago located some 1,500 kilometres from Lisbon and are home to some 240,000 Azoreans.

'The event was not felt in the region,' said the Azores's volcanic and seismic activity institute, CIVISA.