The state government will introduce what it describes as the nation's toughest terror laws and plans to keep inmates convicted of terror offences or suspected of having been radicalised behind bars after their sentence is over if they continue to pose a threat.
The state government and intelligence agencies will apply to the Supreme Court for the extension of custodial sentences or supervision by authorities of prisoners who pose a credible threat to the community for up to five years, the Premier announced.
Applications could also be made for inmates charged with offences unrelated to terrorism but who are suspected of having become "radicalised" in jail.
"NSW will be the first state in Australia to address this," Ms Berejiklian said. "We know these are tough laws but unfortunately these circumstances are here because of what we see around the world and around Australia."
The Premier said the policy was "drastic" but would be modelled on existing post-sentencing schemes for violent or sex offenders.
But the NSW Council for Civil Liberties said there was no need for any extension of post-sentencing policies.
"It can only be [a] political [measure]," said President Stephen Blanks. "It's just an abuse of what the courts are there for, which is to find truth.
"This is a regime which will result in the continued detention of people simply for what they say or think. It's fundamentally contrary to the idea of a free society".
The Premier said her government was still considering the details of a federal government proposal to grant its authorities access to states' databases to harvest licence photos that could track suspects using facial recognition technology and surveillance footage.
But Ms Berejiklian said the NSW government generally supported strengthening national security protections.
"All of us have to accept, from time to time, that our civil liberties aren't what they used to be," she said. "I'm keen to support any measure that supports public safety.
"I think all the community would expect us to have a no regrets policy; I don't want us to say what could we have done?
"Sometimes it means all of us have to give up a little bit of our civil liberties.
"It's not a 'maybe' threat; the threat in NSW is probable. When the threat is probable you need to look at what you're doing."
Corrections and Counter Terrorism Minister David Elliott said reports of inmate behaviour and communications would be combined with federal and state intelligence reports to form applications to the court.
"There is judicial oversight," Mr Elliott said. "Not only have we got to get the evidence, the Supreme Court has to evaluate that".
The state government has already tightened bail and parole laws to make it harder for terror suspects to remain in the community and Ms Berejiklian appointed the state's first dedicated Counter Terrorism Minister this year.
"These are thought crimes where the evidence will be given by prison officers with minimal regard to essential legal principles such as the presumption of innocence," he said.
"We're not looking at very large group of people here," said Corrective Services Commissioner Peter Severin.
He said there were no impending cases of terror suspects to be released of which he was aware, but that "we need to have these laws in place so we can target those who are."
In recent years the spread of radical views by inmates convicted of terror offences has been a major concern for corrections authorities and it has spent $47 million on programs to combat prison extremism.
The Premier said the government would refine its sentencing policy reforms until next month.
About six people were currently detained and about 70 were under supervision under post-sentencing orders for other sex and violent crime, according to the state government.