SYDNEY - Residents and tourists on an island off Australia's northeast coast will begin evacuating to the mainland due to a threat posed by a cyclone.

The Bureau of Meteorology said on Thursday that tropical cyclone has reached category three strength and was continuing to move slowly in the Coral Sea off the coast of the state of Queensland.

As of Thursday morning local time, the bureau said the cyclone was about 860 km off the coast of the city of Mackay in Queensland's tropical north.

The bureau said that the cyclone was generating wind gusts of up to 185 km per hour and was strengthening as it moved south.

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"There is high confidence that Alfred will remain well off the Queensland coast into the weekend," it said.

"There is high uncertainty though, in regards to Alfred's movement beyond Saturday, with the possible risk that Alfred may move closer to the central or southern Queensland coast by Sunday."

Residents and visitors on Great Keppel Island, a popular tourism destination about 15 km off the coast of the city of Rockhampton, were set to begin evacuating on Thursday.

The resort said it could reopen on Monday subject to conditions.

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In the city of Bundaberg, 300 km north of Brisbane, the State Emergency Service has begun helping residents secure loose items and made preparations for potential destructive winds, heavy rainfall and flash flooding.