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 (USGS), which initially said the quake had a magnitude of 7.8 before downgrading it to 7.5, said it struck 136 kilometres (84 miles) off the coastal town Gorontalo at a depth of 21 kilometres.

US officials issued a tsunami warning for an area within 1,000 kilometers of the epicentre, but a similar warning from Indonesian authorities was withdrawn shortly after being issued.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 250 kilometres away, had reported collapsed buildings.

`In an earthquake like this I think it`s likely there will be victims,` Indonesian geological official Sutiono said.

The state-run Antara news agency said thousands of people fled their homes and hotel rooms in Gorontalo when the quake struck around 1:02 am (1702 GMT Sunday).

The USGS reported two powerful aftershocks.

The Hawaii-based Pacific Tsunami Warning Center warned that `this earthquake has the potential to generate a destructive regional tsunami along coasts located within a thousand kilometers (620 miles) of the earthquake epicenter.`

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.