Terrorists plotted to blow up Australian aeroplane, says PM Malcolm Turnbull

Four people in custody as airport security beefed up

Police and forensic officers at the scene of a counter-terrorism raid on a property in Sydney (EPA/SAM MOOY)

Australian security services have disrupted a plot to blow up an aeroplane, Prime Minister Malcolm Turnbull has announced.

Police arrested four people in connection with the alleged plan.

Counter-terrorism raids took place took place in Sydney on Saturday afternoon.

Mr Turnbull said they were "designed to disrupt and prevent plans to undertake terrorist attacks in Australia".

It is not known what the specifics were or when the attack was scheduled to take place, but is believed an Improvised Explosive Device (IED) was the intended weapon.

The operation was carried out by the Australian Federal Police, the New South Wales state police and the Australian Security Intelligence Organisation, the country's domestic spy agency.

"Four men have been taken into custody and are assisting police with their enquiries," a police statement said.

Seven Network television reported that 40 riot squad officers stormed an inner-Sydney house before an explosives team found a suspicious device.

Mr Turnbull said he was briefed on the progress of the operation by security agency chiefs.

"My number one priority, and that of my government, is the safety and security of all Australians, and the public should be reassured that our security and intelligence agencies are working tirelessly to keep us safe," the prime minister said in a statement.

Security at airports across the country has been increased after the operation, the Sydney Morning Herald reported. Mr Turnbull advised travellers to get to airports earlier than usual.

At least 70 people have been charged with terrorism since 2014, said Justice Minister Michael Keenan.

He added: "The primary threat to Australia still remains lone actors, but the events overnight remind us that there is still the ability for people to have sophisticated plots and sophisticated attacks still remain a real threat.

"In light of this information, it's very important that everyone in Australia remains vigilant."

Australian Federal Police commissioner Andrew Colvin said the investigation was likely to be “very long and protracted”.