An expert on terrorism and Islam has said that those targeted in the overnight raids were likely motivated by what has been happening in Syria and Iraq rather than in Australia.
Greg Barton, acting director of the Centre for Islam and the Modern World at Monash University, described the raids in two Australian cities as "massive" and the "largest in history".
Australian Prime Minister Tony Abbott has said that the overnight raids were prompted by fears that "demonstration killings" were being planned.
Speaking at a press conference, he said that police acted on intelligence showing directions from "an Australian who is apparently quite senior in ISIL ... to conduct demonstration killings here in this country".
"So this is not just suspicion, this is intent and that's why the police and security agencies decided to act in the way they have," he said.
Speaking at a press conference, police said they had detained 14 individuals and charged one person with serious terrorism offences.
They confirmed that 800 police officers were involved in the operation.
Residents in several suburbs of Sydney and Brisbane say they were woken by the sound of hovering helicopters and police using loudspeakers in the early hours of Thursday morning.
One resident, Mark Anderson, told Fairfax Media he heard police officers on a loudspeaker asking someone to come outside a home in the Guildford suburb of Sydney.
This is the first video ITV News has received showing the raids:
The acting head of police in Australia has said that dawn raids in Sydney and Brisbane were not directed at a specific threat, but rather "random acts against members of the public".
Police believe that this group that we have executed this operation on today had the intention and had started to carry out planning to commit violent acts here in Australia.
Those violent acts particularly related to random acts against members of the public.
Hundreds of heavily armed counter-terrorism police raided homes in the Australian cities of Sydney and Brisbane before dawn on Thursday.
Last week, Australia raised its terror threat level to 'high', citing the likelihood of terrorist attacks by Australian citizens radicalised in Iraq or Syria.
Up to 160 Australians have either been involved in the fighting or actively supporting it, officials say, and at least 20 have returned to Australia after fighting in the Middle East.
The mother of shark attack victim Paul Wilcox has spoken about her sorrow at the loss of her son and said her "only comfort is he died rather than be injured (or) maimed".
Marie Wilcox, of North Wales, spoke to the BBC after her 50-year-old son was killed by a shark off the shore of Australia's Byron Bay on Tuesday.
Ms Wilcox said: "I had a happy, well-adjusted lovely son talking to me the day before. Twenty-four hours later he is dead and I still cannot take it in."
Mr Wilcox, who reportedly emigrated from the UK to Australia almost 30 years ago, had previously lived in Sydney before moving to the popular resort town of Byron Bay.
A 50-year-old man who was killed in a shark attack off the Australian coast near Byron Bay has been named as British expat Paul Wilcox.
Mr Wilcox was attacked by what was believed to be a great white shark at 10.40 am local time on Tuesday, while his wife Victoria walked on the beach.
According to The Sydney Daily Telegraph, Mr Wilcox was originally from Warwickshire and had previously lived in Sydney before moving to Australia's Gold Coast.
A man has been killed in a suspected shark attack at Byron Bay, the popular tourist destination on Australia's east coast, officials said.Read the full story ›
An Australian man has been charged with sexually abusing twins he fathered with a Thai surrogate when they were aged under 10, according to ABC News.
The man, who cannot be identified, has been charged with indecent dealings of a sexual nature with the twins and possessing child abuse material which was discovered after a raid on his property.
The man denies all of the allegations against him, the report said.
Australian child welfare authorities are now looking into sending the children back to Thailand to be with their surrogate and biological mother.
However, the twins "consider themselves to be fully Australian" and "don't know that they are half Thai or have any connection to Thailand", Childline Thailand's Ilya Smirnoff told the website.
He added that paedophiles were "abusing" the surrogacy system in Thailand. The country is currently working on new laws banning commercial surrogacy.