Tamil Khaja, 20, pleaded guilty to preparing for or planning a terrorist act

A young would-be terrorist said he 'wouldn't buckle' at firing at a two-month-old baby or someone carrying the infant, a Sydney court has been told.

Tamil Khaja, 20, who's pleaded guilty to preparing for or planning a terrorist act, had begun to scope out potential target buildings in Sydney including the Parramatta District Court precinct and Timor Army Barracks.

At his sentence hearing in the Supreme Court at Parramatta on Friday, the prosecutor tendered an agreed statement of facts which included the baby comments made to two undercover police officers.

Court documents show Khaja said 'maximum fire, I mean to take as many of them down as I can, and at the end when I see that there's too many I will take myself with them as well', Nine News reported.

He said he 'wouldn't buckle' at firing at a two-month-old baby or someone carrying the infant, a Sydney court has been told

Khaja was 18 at the time, and also told police 'there's Kirribilli House... I've looked at the house that's in Canberra as well'.

He was arrested in May 2016 during a joint NSW and Federal Police operation for sizing up potential target buildings and previously attempting to travel to Syria.

Khaja allegedly tried to travel to Syria but was stopped at Sydney Airport because his passport had been cancelled.

Police believe he was acting alone in planning a terror attack in Sydney.