The storm was skirting the coast from just southwest of Darwin to the Kimberly Coast for the second week, and was expected to intensify to hurricane force as it moved into the open waters of the eastern Indian Ocean on Christmas Day.

On Tuesday, the cyclone was producing winds of up to 74 mph (120 km/h) and sea swells up to 13 feet (4 meters), the Bureau of Meteorology reported on its Web site

Some staff of petroleum exploration rigs off the coast were evacuated as a precaution, but there were no reports damage to the rigs or any onshore facilities due to the cyclone.

A spokesman for the Stag and Ocean Legendre offshore oil platforms, which together produce 13,200 barrels per day, told the Australian Associated Press that the facilities had been shut and workers evacuated to the mainland.

"It's a normal precautionary measure as part of standard operating procedures," David Parker told the agency.

Cyclone Billy Track

Satellite Loop: University of Wisconsin