A Chinese spy ship has been spotted off Australia's western coast.

Australia's Defence Minister Peter Dutton says the vessel was seen near a naval communications base.

The ship was most recently cited at 6am local time today, and was 250 nautical miles north-west of Broome. The Australian Defence Force has been tracking the spy ship for the last "week or so".

The vessel had entered Australia's exclusive economic zone.

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Dutton said the ship was "unusual" in that it had come so far south, and had been "hugging" the coastline.

"We haven't seen a ship from that maybe come this far south and is tracking up towards Darwin at the moment."

Dutton said Australia had recently put planes in the air and deployed other surveillance techniques.

"I think people understand the difficulty, the reality, of the Indo-Pacific at the moment, the acts of aggression from the Chinese leadership and from the Chinese government," he said.

"I think Australians deserve to know what is taking place and it is a repeat of a previous practice where we have made the public aware of these activities before."