A new phone and online support service for those who are worried people they know may be at risk of radicalisation or violent extremism has finally been launched.

The New South Wales Government has defended the time it had taken to set up the Step Together phone and online support service.

It was announced more than 18 months ago as part of a suite of measures in the wake of the fatal shooting of police employee Curtis Cheng by 15-year-old Farhad Jabar at Parramatta.

During that time, governments around the world have been under pressure to do more to combat radicalisation, as low-tech terrorist attacks hit Melbourne, London and several European cities.

Counter Terrorism Minister David Elliot said more than 240 community groups were consulted about the design and function of the Step Together service.

"This is new territory for western worlds and we have to make sure that we tread carefully so we don't do more damage than good," he said.

He said it was important to set up a service that families felt comfortable calling without fearing the consequences.

"This is a support line, not a report line — this is to provide support and advice to individuals who are concerned," Mr Elliot said.

But he acknowledged that if the counsellors at the service became aware of a serious or imminent risk, information may be passed on to authorities.

"We have legal obligations to report information as citizens of this country," he said.

"If your loved one is showing signs of violent extremism ... it's better now you get advice and seek support than in the future when they could be facing a lifetime in prison."

The Government said the phone line was equipped to deal with concerns about different kinds of radicalisation, including people whose relatives are involved in far-right or religious extremism.