JAKARTA (AFP) - A major 7.5-magnitude earthquake struck off Indonesia's Sulawesi island early Monday morning, destroying houses and triggering a tsunami warning, officials said. The US Geological Survey, which initially said the quake had a magnitude of 7.8 before donwgrading it to 7.5, said it struck 136 kilometres off the coast of the central island of Sulawesi at a depth of 21 kilometres. US officials issued a tsunami warning for an area within 1,000 kilometres of the epicentre, but a similar warning from Indonesian authorities was withdrawn shortly after being issued. Indonesian officials said there were no immediate reports of deaths but residents in Tolitoli, around 250km away had reported collapsed buildings. The Hawaii-based Pacific Tsunami Warning Center warned, "This earthquake has the potential to generate a destructive regional tsunami along coasts located within a thousand kilometres of the earthquake epicentre." It advised that authorities in the region "take immediate action to evacuate coastal areas." "This earthquake is located outside the Pacific. No tsunami threat exists to coastlines in the Pacific," it added. Indonesia launched a new hi-tech system on Tuesday aimed at detecting a potential tsunami and providing faster alerts in a region battered by frequent earthquakes. The sprawling archipelago of some 17,000 islands, which lies in the seismically-active "Pacific Ring of Fire", was hit by a devastating tsunami four years ago that left an estimated 170,000 people dead or missing in Aceh province. A moderate 5.7-magnitude earthquake also hit off the coast of India's Andaman islands in the Indian Ocean on Sunday, the US Geological Survey said. The USGS said the epicentre of the quake, which hit at 1250 GMT, was 143km southwest of Port Blair.  There were no immediate reports of casualties or damage, the Press Trust of India agency reported.