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Genetic testing shows they are not linked to ants from the Queensland outbreak. (Supplied)
In short:
A red imported fire ant nest has been discovered at the Enfield Intermodal Logistics Centre in Sydney's inner west.
No other nests have been discovered.
The government has launched an awareness campaign so nearby residents and businesses can be on the lookout for them.
A biosecurity response has been activated in Sydney's inner west after a red imported fire ant nest was discovered at a key freight industry logistics and warehousing facility.
The NSW government said Commonwealth authorities discovered the fire ants at the Enfield Intermodal Logistics Centre in a lure used as part of their detection system.
The ants are 2-6 millimetres long and are a dark red-brown colour and live in nests in the ground.
Their sting causes a painful, fire-like burning sensation and leads to swelling and redness that can develop itchy blisters or pustules that take days to improve.
Specialist fire ant detection dog teams were deployed to the site and a nearby area with no other nests discovered.
Genetic tests confirmed the fire ants were likely to have originated from overseas via a container and not from south-east Queensland, where there is an infestation.
An area under the shipping container where the ants were found. (Supplied: NSW government)
An incident management team was established including NSW Department of Primary Industries and Regional Development experts and Queensland-based officers from the National Fire Ant Program.
The NSW government said it would work with the local community to raise awareness about the insects in coming days so people could be on the lookout for them.
Fire ant detection dogs found no other nests. (Supplied: NSW government)
"The immediate focus is on inspecting properties and treating any potential location within a 500-metre radius of the Intermodal Centre, then undertaking surveillance and treatment where required in the surrounding 2km radius," the statement said.
"These distances are based on scientific understanding of how queen fire ants can move and potentially establish a new nest."
The government said biosecurity teams successfully eradicated fire ant nest incursions in NSW's Northern Rivers over the last three years and at Port Botany in 2014.
Invasive Species Council advocacy director Reece Pianta said biosecurity measures found the insects before they had the chance to become an established infestation.