Four people were arrested in a series of raids across Sydney on Saturday which the prime minister said were carried out to foil plans for terrorist attacks in Australia.

Armed police stormed homes in at least four neighbourhoods, including in the inner city.

“The New South Wales Joint Counter Terrorism Team has conducted multiple searches across Sydney today, resulting in the arrest of four men,” police said in a statement.

“These searches and the broader investigation remain ongoing, and further information will be made available at the appropriate time.”

The Seven Network reported 40 riot squad officers moved on one inner city home before an explosives team found a suspicious device, although police would not confirm this.

TV footage showed a man with a bandage on his head and draped in a blanket being led away by authorities.

National broadcaster ABC quoted a woman as saying her son and husband were arrested in the raids, but denied they had links to terrorism.

“I love Australia,” she said as she was led away to a car.

Prime Minister Malcolm Turnbull urged people to “remain alert”.

“These operations are designed to disrupt and prevent plans to undertake terrorist attacks in Australia,” he said of the raids.

“I have been kept closely briefed on the progress of the operations by the heads of our relevant security agencies.

“However, as the operations are ongoing, it is inappropriate to provide further detail at this stage.”

Australian officials have grown increasingly concerned about the threat of extremist attacks and have prevented 12 on home soil since September 2014, with more than 60 people charged.

But five have taken place, mostly with guns, including a fatal shootout in Melbourne in June claimed by the Islamic State group.

In that incident, a man of Somali background was killed in a gun battle with police when he opened fire following an hour-long standoff after taking a woman hostage.

It is alleged 29-year-old Yacqub Khayre, linked to a 2009 terror plot targeting an Australian army barracks, had first murdered a Chinese-born Australian man.

AFP