"My aim is to go to Friday prayer in a packed mosque," Cormac Patrick Rothsey allegedly wrote on Facebook on Wednesday, according to a statement of police facts. "No turning back when called to prayer."

But it was a post on Thursday afternoon, the culmination of days of increasingly violent anti-Islamic rhetoric espoused on Mr Rothsey's Facebook page, that was deemed such a significant threat that Joint Counter Terrorism police launched a major operation to locate and arrest the 43-year-old.

"Australia Cormac Rothsey mosque raid soon," Mr Rothsey allegedly wrote on Facebook. "Make ya movie (sic). "No turning back."

That "imminent threat", that Mr Rothsey would attack a mosque and kill worshippers, prompted a major police operation, led by Counter Terrorism Police from the NSW Joint Counter Terrorism Team with all officers in Newcastle and the Central Coast put on alert.

But Mr Rothsey's current itinerant lifestyle made him difficult to locate, police said.

At 3.54pm on Thursday, Mr Rothsey allegedly wrote: "F---in' hell. Let's do it."

At 5.10pm, heavily armed specialist tactical police moved in and arrested Mr Rothsey in Beaumont Street, Hamilton.

He was later charged with using a carriage service to menace, harass or offend.

He applied for bail in Newcastle Local Court on Friday, but it was refused due to the unacceptable risk he posed to the community.

Police say Mr Rothsey first came to their attention on August 27 when a report was made to the National Security Hotline about two Facebook profiles espousing anti-Islamic rhetoric.

Investigators say they dug into the Facebook profiles and identified Mr Rothsey was a man "with an intense hatred for Muslims and those who show compassion or support for the Islamic community".

On Monday, Mr Rothsey allegedly posted a picture of an atom bomb along with the words: "Dear Mr Trump, can you please give this gift to Lakemba for Ramadan."

But as police monitored his Facebook profiles in the following days, they allege there was a shift from posting violent, nationalist, racist and anti-Islamic content to a gradual focus on a stated intent to kill or injure Muslims in a mass casualty attack.

"I will do big damage," Mr Rothsey allegedly wrote. "I don't give a f--- about my life." After his arrest, Mr Rothsey allegedly admitted to making a number of violent and derogatory comments but said he "gets that way" after he drinks alcohol.

He allegedly acknowledged the posts would cause police to be concerned but said he had no weapons and would never act on them.