Prime Minister Malcolm Turnbull has confirmed that major counter-terror raids in Sydney have disrupted a plot to bring down an aircraft.
Speaking after the arrest of four people in a joint-agency operation, Mr Turnbull said the raids demonstrated the government's commitment to keeping the Australian people safe.
"Last night there has been a major joint counter-terrorism operation to disrupt a terrorist plot to bring down an airplane," Mr Turnbull said.
"The operation is continuing. At this stage, four people have been arrested and a considerable amount of material has been seized by police.
"This is an example of the outstanding work that is conducted by the joint counter-terrorism team, which consists ... of the Australian Federal Police, the NSW Police, ASIO, and the NSW Crime Commission."
Mr Turnbull said extra security measures were implemented at Sydney airport on Thursday, which have since been extened to all domestic and international airports across the nation.
He said travellers should be aware of extra security screeening at airports.
"It is important that Australians are aware of the increased threat. (But) be assured we have the finest security and intelligence services in the world and they are working ... night and day to keep Australians safe."
Australian Federal Police, NSW Police and the domestic spy agency ASIO jointly carried out Saturday's raids in the suburbs of Surry Hills, Lakemba, Wiley Park and Punchbowl.
Police said four men were taken into custody and are assisting police with inquiries.
Australian Federal Police Commissioner Andrew Colvin said officers became aware people in Sydney were planning to commit a terrorist attack using an "improvised device".
The Seven Network reported that 40 riots squad officers stormed a Surry Hills terrace before an explosives team found a suspicious device.
TV footage showed a man with a bandage on his head and draped in a blanket being led away by authorities.
The family who lived in the raided house on Cleveland Street in Surry Hills have been described as "perfectly nice and normal people" by a neighbour.
"We knew them to say hello to and they seemed nice," a woman in her early 30s, who didn't want to be identified, told AAP.
An elderly couple lived in the home, the neighbour said, and they had adult children.