Tropical cyclone Iggy strengthened to a category two storm and was moving towards Australia's northwest coast on Friday, threatening the region's rich mining fields after shutting down more than 54,000 barrels a day of offshore oil production.

Cyclone Iggy was upgraded from a category one storm and was about 600 km (370 miles) northwest of Exmouth by 0746 GMT, Australia's Bureau of Meteorology said on Friday.

Category two is the second lowest of five ratings, denoting cyclones that pack destructive wind gusts of 130 km/h (80 mph) at their centre. The system is intensifying and is expected to become a category three storm by late Saturday, the weather bureau said in a statement on its website (http://www.bom.gov.au).

The storm was slowly moving towards the Pilbara coast and its major iron ore shipping facilities.

Over the next 72 hours TC Iggy will steadily intensify while moving southeastwards towards the western Pilbara coast, the bureau said.

Strong winds, heavy rainfall and abnormally large swells will be experienced near Christmas Island, the Kimberley and Pilbara coasts.

Companies, including Rio Tinto and BHP Billiton, have major iron ore mining operations in the Pilbara region.

Australia's Woodside Petroleum, which suspended production at some offshore fields on Wednesday due to the storm, said on Friday it had shut oil production at its Vincent, Cossack, Wanaea, Lambert and Hermes oil fields off the northwest coast.

Woodside's Vincent oil field produced just under 14,000 barrels per day (bpd) in 2011.

Apache Corp had also suspended some oil production, including at the Ningaloo Vision, the floating production, storage and offloading vessel that produces oil from Apache's Van Gogh oil field.

The Ningaloo Vision has a production capacity of 63,000 bpd although output at the Van Gogh field is 40,000 bpd. Apache said on Wednesday it was prepared to move the Ningaloo off site at short notice.

Tropical cyclones and temporary shutdowns are a normal part of Australian summers, but an especially stormy season can have major impacts, such as when cyclones and flooding swamped the coal-mining industry in the country's northeast a year ago.

Tropical cyclone Heidi lashed the remote northwest earlier this month, shutting the major iron ore terminal at Port Hedland.

State Emergency Service advises that there are no community alerts at present, said the weather bureau.

(Reporting by Lincoln Feast; Additional reporting by Nallur Sethuraman and Soma Das in BANGALORE; Editing by Clarence Fernandez)

(Corrects capacity in lead and bullet to 54,000 bpd and Ningaloo Vision's capacity in paragraph 11)