Keeping a Sydney teenage terrorism suspect in Australian Federal Police (AFP) custody without charge could amount to a form of torture, lawyers say.

The 18-year-old man, who cannot be named, was arrested on Wednesday morning during counter-terrorism raids in connection to last week's fatal shooting outside New South Wales police headquarters at Parramatta, in Sydney's west.

He was one of four young males arrested during large-scale raids in four Sydney suburbs.

The other three men were released without charge on Wednesday evening.

Under normal circumstances the AFP can detain a suspect without charge for up to 24 hours.

However, in 2004 Part 1C of the Crimes Act was beefed up to allow police to apply to the courts for extra time to detain and question a terrorism suspect.

Yesterday afternoon, the AFP's lawyers won a last-minute, closed-court hearing that granted them another 100 hours to question the 18-year-old.

Australian Lawyers Alliance spokesman Greg Barns said the use of anti-terrorism laws has concerned his organisation for more than a decade.

"The difficulty with these laws is that the AFP or state police can get permission from a court to get 100 hours of questioning in circumstances where that 100 hours can be spread over a number of days," he said.

"So they could theoretically do two or three hours today, they could do another 10 hours over the weekend and well into next week.

"It's extremely concerning for a number of reasons; firstly, this young man is a youth.

"Secondly, the rights of lawyers in these types of cases to ensure that their client is safe are extremely limited, and thirdly, you have to say that any information that's gathered from a person in circumstances where they've been held incommunicado, they are young and vulnerable you have to wonder about the quality of any information that is gathered.

"It in some circumstances could certainly amount to torture."

Four people were arrested in terror raids in Sydney on Wednesday morning. ( AAP: NSW Police )

The legal provision has previously allowed Queensland doctor Mohammad Haneef to be detained in July 2007 for 12 days on suspicion of involvement in a terrorist attack on Glasgow airport.

The case against Dr Haneef ultimately fell apart and he later won significant compensation from the Australian Government.

The president of the New South Wales Council for Civil Liberties, Stephen Blanks, said the Haneef case exposed deep flaws in this legal provision.

"These are the types of laws that bring the authorities into disrepute, and bring the law into disrepute," he said.

"It's the kind of law that is so unfair that the community loses respect for the authorities when these kinds of detention powers are exercised, and you only have to look at the Haneef case to see how that occurs."

Mr Blanks said police should lay charges, or release the teenager quickly.

"Regardless of community safety concerns, we really should not be giving the authorities [power] to take people off the street on mere suspicions without the ability to charge them," he said.

"We live in a free society if you want to go and live in a totalitarian society where the police typically have this kind of power, people can vote with their feet.

"The authorities are subject to the rule of law and people are free until there is appropriate basis for detaining them."

Criminal defence lawyer Chaddy Mardini has represented terrorism suspects, including Ahmad Azaddin Rahmany, who was charged after last year's sweeping counter-terrorism raids.

He said he is concerned that police arrested three other young men on Wednesday in high-profile circumstances, yet ultimately released them without charge.

"You would have thought that if they had the power to raid and arrest, then you would have thought they had the information or evidence to lay a charge that would stick.

"It's almost like a fishing expedition and they're playing with people's liberty."