SYDNEY, Australia (Reuters) -- Towns along Australia's remote northwest coast were told on Wednesday to prepare for one of the most powerful cyclones ever to threaten the country as it approached with winds of up to 260 km (161 miles) an hour.

Tropical cyclone Rosita was upgraded to a category four cyclone, the second highest in a ranking scale of five, from a category three late on Wednesday.

A Bureau of Meteorology spokesman said Rosita was expected to hit land near Broome, 1,700 km north of Western Australia state's capital Perth, at about midnight (1600 GMT).

"Gales with gusts up to 100 km per hour are expected to develop on the coast later today ... with very destructive winds with gusts to 260 km per hour near the cyclone center tonight," the spokesman said.

The spokesman told Reuters the storm, which has already disrupted oil producers in the region, was also expected to bring flooding rains and storm tides with damaging waves.

He said Rosita was the strongest storm to approach land since Cyclone John, the most powerful cyclone ever to hit Australia, blasted ashore last December.

John hit a sparsely populated area of the northwest coast but still ripped roofs from houses, uprooted trees and cut communications with small towns in Western Australia's Pilbara mining region.

Storm tide warnings

Rosita was about 140 km west of Broome and moving southeast at 15 km an hour at 4 p.m. (0800 GMT). The storm was expected to cross the coast between Broome and Port Hedland to the south.

Australia houses several hundred illegal immigrants, including a handful of Kosovo refugees who last week refused to return home, at a permanent detention facility in Port Hedland.

Emergency services officials said residents of coastal towns in the area had been warned to expect dangerous storm tides.

"I think we have got an eight-meter (26 feet) high tide tonight, which is a bit of a concern with the cyclone coming down," emergency services spokesman Gordon Tiddums said.

He said tourists in the area had been warned not to try to reach Broome.

Chevron Australia, operator of the Barrow Island field about 100 km (62 miles) off the coast south of Port Hedland, said a tanker due to arrive for loading on Tuesday had been delayed until Saturday because of the storm.

"Because of the swell and the unsettled conditions they have made a decision not to berth tankers at this point," a spokeswoman for the Chevron Corp unit said.

Rosita's landfall was expected to be well clear of the major offshore oil producing region southwest of Port Hedland.

Woodside Petroleum Ltd said on Tuesday it had cut output from the Cossack oil field to 80,000 bpd from 140,000 bpd as Rosita approached.

Iron ore miners The Broken Hill Pty Co Ltd and Rio Tinto Ltd/Plc said on Wednesday they were monitoring Rosita's approach. Port Hedland is BHP's iron ore port, with Rio's port further south at Dampier.

http://cnn.com/2000/WEATHER/04/19/weather.australia.reut/index.html