Urgent investigation after foiled Sydney terror threat

Suspects arrested over a foiled terror plot across the Tasman may have aimed to poison an entire plane-load of people.

Four men are in custody and travellers at Australian airports are facing long delays as tightened security measures bite.

Details are still emerging, but this was no ordinary terror plot.

Reports suggest four men arrested yesterday were planning to use poisonous gas on the flight from Sydney to the Middle East killing hundreds of people on board.

Today police combed through their raided properties seizing smartphones, tablets and a boarding pass for a recent flight from Indonesia to Sydney.

They're also understood to have found a meat grinder which could have housed a potential bomb built with the help of Islamic State.

No charges have been laid, but investigators have been granted extra time: seven days to interrogate the men in custody and uncover every aspect of the plot.

In the meantime, Australia's on high alert. Peter Dutton, Border Protection Minister says "the security threat to our nation is as prevalent as it's ever been".

It's the 13th foiled terror plot in Australia, but this attempt is one of a kind.

The country's accustomed to lone wolf attacks, but not organized terror cells.

The new level of threat and sophistication is prompting a new urgency of response.