NSW Police Force, Australian Border Force and US Homeland Security Investigations (HSI) commenced an investigation last month after receiving information in relation to the alleged importation of firearm parts and drug manufacturing equipment into Australia from the US, Hong Kong, China, Germany and Japan.

Following extensive investigations, police officers from Western Region Enforcement Squad and investigators from Border Force and Homeland Security executed a search warrant and a customs search and seizure warrant at a home at South Bathurst just after 6am today.

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The operation is also being assisted Chifley Police District, the Dog Unit, and Western Region Operations Support Group.

After investigators uncovered a suspicious substance inside the home, assistance was requested from Fire and Rescue NSW's HAZMAT to render the area safe.

Specialist officers from the Rescue and Bomb Disposal Unit and the Drug and Firearms Squad's Chemical Operations Unit are in attendance.

The 36-year-old male resident was served with Firearms and Weapons Prohibition Orders before being arrested and taken to Bathurst police station, where he is expected to be charged.

The operation is ongoing and further information will be provided when it becomes available.

Information about the importation of firearms, illicit drugs or other prohibited items can be reported to BorderWatch: https://www.homeaffairs.gov.au/about-us/what-we-do/borderwatch/reporting.

EARLIER: A 50-METRE exclusion zone remains in place around a South Bathurst home following the discovery of an "unknown substance" this morning.

Officers from Australian Border Force, US Homeland Security Investigations and NSW Police are involved in the joint agency operation, which police have stated is not related to counter terrorism.

Officers moved in around 6am on Wednesday, supported by NSW Fire and Rescue and NSW Ambulance.

Bathurst police station officer-in-charge, Inspector David Abercrombie, has just addressed the media gathered at the scene near the intersection of Violet and Prospect streets, but could not reveal many details at this stage.

"The operation is on-going and we can't discuss any details at this stage," Inspector Abercrombie said.

"During the course of the operation police discovered an unknown substance and had concerns about it. The NSW Fire and Rescue's HAZMAT unit was called in to assess the substance.

"Police decided to enforce a 50-metre exclusion zone around the property which included a neighbouring house and one behind.

"One of the properties was vacant while the other had people in it who have been evacuated."

Inspector Abercrombie said police had called on specialist resources to assist in the operation, including a Sydney-based bomb disposal squad which arrived at around 11am and the NSW Police Force's chemical operations unit.

Inspector Abercrombie would not be drawn on how authorities became aware of the property, nor what involvement US Homeland Security had with the operation.

Specialist police were still in the process of determining what the substance found the house could be.

"We don't know what it is. It's an unknown substance which could be dangerous to police and residents around the property," Inspector Abercombie said.

He said more details would be released this afternoon.

EARLIER: A JOINT operation involving Australian Border Force officers and US Homeland Security is under way in South Bathurst, with residents urged to avoid the area.

Officers descended on the area around Violet Street, opposite Jacques Park, around 6am on Wednesday and taped off a number of streets.

However, a spokeswoman for NSW Police stressed the operation was "not related to counter terrorism" and said there was no immediate threat to residents.

"A joint agency operation which involves the NSW Police Force, Australian Border Force and US Homeland Security Investigations commenced about 6am at a home at South Bathurst," the spokeswoman said.

"Investigators are also being assisted by Fire and Rescue NSW and NSW Ambulance.

"Members of the community are urged to avoid the area at this time.

"The operation does not relate to counter terrorism and there are no current risks to the safety of the community."

It is not known at this stage how long the operation is likely to continue.

A number of residents from nearby homes are watching the operation unfold from inside their homes, or while standing in the street.

One neighbour, who asked not to be named, said it was "a sight to wake up to".

"All these police and border protection, I just thought, 'oh my god what is happening'," he said.

Another man said he was coming down Propsect Street around 7am and found the road blocked off by one unmarked car and the three marked police cars.