BREAKING NEWS: Sydney teenager arrested over alleged Anzac Day terror plot

Police believe a 16-year-old Sydney boy was acting alone in an alleged terror plot to coincide with Anzac Day.

"At this stage we believe it was one person by himself," NSW Police Commissioner Andrew Scipione told a media conference shortly after the Martin Place dawn service on Monday.

"The risk from this particular threat has been thwarted."

The boy was alone when he was arrested by officers from the NSW Joint Counter Terrorism Team on Sunday.

He's been charged with one count of acts in preparation for, or planning, a terrorist act, that carries a maximum penalty of life imprisonment.

He was remanded in custody to appear in a children's court later on Monday.

Mr Scipione would not give any details of the alleged plot, saying it would become clearer after the court appearance.

"We knew of this particular young person but these are facts that will come before the courts when he is presented today," he said.

The boy's family home at Auburn has been searched.

"There was a search conducted and a number of items looked at. I'm not in a position to tell you if anything was seized."

Both Mr Scipione and AFP Commander Chris Sheehan said the boy's age was troubling.

"It is important for families to stay on top of what's happening, particularly as they see changes in behaviour," Mr Scipione said.

The commissioner urged people to attend Anzac Day services.

"Do not let an event like this stop you from going out and taking part in what is a most important commemorative day for us," he said.

"So, please, don't be perturbed."

NSW Premier Mike Baird said the events were disturbing and praised police for the arrest.

"The important point is not to look at the hypotheticals, but to look at the actions that have been taken. Actions were taken by police to prevent actions, to keep us safe," he told reporters after the dawn service.

He, too, urged people to commemorate Anzac Day.