Australia has raised the alarm over a Chinese warship with spying capabilities which it claims has been stalking the country's western coast for the past week.
Peter Dutton, Australia's defence minister, criticised Beijing's "aggressive act" and said his country’s navy would continue to monitor the vessel.
It comes just weeks after the Communist Party ruled state signed a security pact with the Soloman Island, increasing tensions between Australia and China.
Beijing has also in recent years been building up its presence in the South China Sea, where Australia has significant interests, both economically and in terms of freedom of trade and navigation.
China insisted the pact was not directed at "any third party". Australia said it was "disappointed" that the Solomon Island had chosen to forge closer links with China.
Speaking at a press conference on Friday morning, Mr Dutton said: "I think it is an act of aggression. I think particularly because it has come so far south,
"It has been in close proximity to military and intelligence installations on the west coast of Australia."
Australia had tracked the spy ship over the past week as it sailed past the Harold E Holt naval communications station at Exmouth, which is used by Australian, US and allied submarines.
Prime minister Scott Morrison said the Chinese navy vessel was not in Australian territorial waters but its presence was "concerning".
"It is clearly an intelligence ship and they are looking at us and we're keeping a close eye on them," he told reporters.
China's embassy in Australia did not respond to a request for comment.
Australia holds a national election on 21 May and the question of a national security threat posed by China has been a campaign theme.
Mr Dutton questioned the "strange timing" of the vessel's appearance although home affairs minister Karen Andrews declined to link it to the election campaign.
The opposition Labor Party said it was seeking a briefing from the government.
Chinese navy vessels have been tracked off Australia's north and eastern coasts several times in recent years, and the same Chinese vessel monitored Australian navy exercises with the US military off the east coast last year.
In February, China and Australia exchanged accusations over an incident in which Australia said one of its maritime patrol aircraft detected a laser directed at it from a People's Liberation Army Navy vessel.
On the latest incident, Australia's defence department said in a statement the Dongdiao Class Auxiliary Intelligence ship named Haiwangxing travelled down the west coast, crossing into Australia's Exclusive Economic Zone on 6 May, and coming within 50 nautical miles of the communications station on 11 May.
The EEZ is 200 nautical miles from the coast, while territorial sea is within a 12 nautical mile limit.
"I certainly don't believe that when you take it together with the many other coercive acts and the many statements that have been made which have been attacking Australia's national interests, you could describe it as an act of bridge building or friendship," Mr Morrison said.
