JAKARTA - An 8.2-magnitude aftershock struck off the coast of Indonesia's Sumatra island on Wednesday, following a stronger quake that triggered an Indian Ocean-wide tsunami alert.

The US Geological Survey said the aftershock struck at 10:43 GMT (6.43pm Singapore time), 615 km (382 miles) from Banda Aceh. The latest aftershock raised a new tsunami alert.

Victor Sardina, a geophysicist with the US Pacific Tsunami Warning Center in Hawaii, told AFP the first tsunami was "not anywhere near" as large as the devastating waves that struck Asia in 2004 and Japan last year.

He said the tsunami measured a mere 35cm near Padang, Indonesia, but could swell to as high as a meter near Sri Lanka, adding that US scientists were still carefully monitoring the situation.

Earlier, the centre said "earthquakes of this size have the potential to generate a widespread destructive tsunami."

A first aftershock measuring 6.5 on the Richter scale was reported earlier.

Indonesia's president Susilo Bambang Yudhoyono has been reported as saying that there is "[n]o tsunami threat although we are on alert from earthquake off coast of Banda Aceh."

Southeast Asian nations issued tsunami alerts and urged people to move to safety away from coastlines after the initial 8.6-magnitude earthquake struck off Sumatra.