April 23 (Bloomberg) -- Australia's far north is set to be lashed by ``very destructive'' winds tonight as Tropical Cyclone Monica, categorized as the most severe, passes just to the north of the Arnhem Land coast, the Bureau of Meteorology said.

The cyclone, which prompted the shutdown of Alcan Inc.'s alumina refinery at Gove, was upgraded to Category 5 late yesterday. The bureau today warned of ``dangerously high tides'' that may cause ``extensive flooding'' along part of the coast and ordered the sounding of emergency sirens in the Gove area, including the town of Nhulunbuy.

Arnhem Land is land belonging to Aboriginal communities. About 200 residents of Nhulunbuy, which was spared the worst of the cyclone, sought protection at the town's cyclone shelter, Australian Broadcasting Corp. said on its Web site. Schools in the area will be closed tomorrow, it said.

``The cyclone should remain close to its current intensity as it moves further west, just north of the north coast overnight,'' the bureau said.

Tropical Cyclone Monica was about 110 kilometers (68 miles) north-east of Nhulunbuy and moving west at 12 kilometers (7.5 miles) an hour at 5 p.m. local time today, the bureau said on its Web site. The cyclone has wind gusts as high as 350 kilometers an hour near its center.

Work Stopped

Alcan, the world's second-biggest aluminum producer, yesterday warned customers of potential interruptions to supplies on contracts from its Gove refinery. Work has also stopped on a $1.3 billion expansion to almost double alumina production at the site.

The Montreal-based company intends to resume production and work on the expansion project ``as soon as weather conditions stabilize and it is deemed safe to do so,'' Jacynthe Cote, chief executive officer, Alcan Bauxite and Alumina, said in an April 22 statement on Alcan's Web site.

All employees have been sent home from the site apart from a skeleton crew of 24 people to manage the refinery during the cyclone, Alcan Gove said today in an e-mailed statement. The company is unable to estimate when production may resume, said Jennifer Shepherd, a spokeswoman for Alcan in Australia.

Monica, which will probably miss the northeastern coast of Arnhem Land, is expected to hit the northwestern coast of the region tomorrow before weakening slightly as it passes over the base of the Cobourg Peninsula, the Bureau of Meteorology said.

The Bureau of Meteorology issued a ``cyclone warning'' for coastal and island communities between Cape Shield and Point Stuart, including Nhulunbuy. It issued a ``cyclone watch'' for areas including Darwin, the capital of the Northern Territory.

A ``cyclone warning'' advises of gale force or stronger winds during the next 24 hours, while a ``cyclone watch'' warns of possible gale force or stronger winds within 24 to 48 hours.

Cyclone Larry, the most powerful storm to hit Australia in 30 years, last month struck Queensland state with winds of 290 kilometers an hour, wiping out more than 90 percent of the nation's A$350 million ($260 million) banana industry.

To contact the reporter on this story: Angela Macdonald-Smith in Sydney at amacdonaldsm@bloomberg.net