UPDATE: TROPICAL Cyclone Rusty has intensified and is expected to unleash a significant storm surge in northern Western Australia.

Authorities are warning residents in low lying areas to evacuate with a threat of flooding, high winds and a coastal tide.

People in low lying areas of Port Hedland including a small section of Pretty Pool should relocate now, states an emergency relocation order, issued on Tuesday morning by the Department of Fire and Emergency Services.

"Rapid and powerful flooding is very likely as Severe Tropical Cyclone Rusty crosses the coast."

The Bureau of Meteorology says the cyclone has increased to a Category 3 overnight and, at 5am (WST), was estimated to be 170km north-northeast of Port Hedland and 320km northeast of Karratha.

The cyclone is moving at eight kilometres per hour towards the coast.