By Morag MacKinnon
PERTH, Jan 30 (Reuters) - A tropical cyclone gathered strength as it headed for the northwest coast of Western Australia on Saturday, forcing ports to close and mining companies to evacuate.
Cyclone Stan, the first of a season which runs from November to April, was estimated to be 195 km (120 miles) north of Port Hedland and moving southeast, the Australian Bureau of Meteorology said.
It is forecast to intensify and cross the coast northeast of Port Hedland, the world's largest iron ore export hub, late on Saturday.
"Very destructive winds with gusts to 170 km/h are possible near the cyclone centre as it makes landfall later on Saturday or early Sunday," the weather bureau said.
It has issued communities in Port Hedland and Dampier and surrounding coastal and inland areas with a yellow alert, meaning they need to move to shelter.
The bureau also warned of a potential dangerous storm tide with "damaging waves and dangerous flooding".
The ports of Dampier and Port Hedland, through which gas from the northwest shelf and almost half of the world's seaborne iron ore are shipped, were closed, authorities said.
A BHP Billiton (L:BLT) BHP.AX spokesman said the company was closely monitoring the cyclone.
"All tie-down activities have been completed and staff have been evacuated with a minimal number remaining for security and observation purposes," the company said in a statement.
The Port Hedland facility also ships cargo for Fortescue Metals Group FMG.AX , while Rio Tinto (L:RIO) RIO.AX ships iron ore through Dampier.