The terror threat level in Australia is now 'probable'. But what do these levels mean?

Following yesterday’s terror attack in Manchester, the terror threat level in the UK has reached “critical” for the first time in a decade.

That means a terrorist attack is expected imminently, with Prime Minister Theresa May explaining the attacker responsible for the death of 22 people may have been a part of a network of terrorists.

In Australia, the terror threat level is currently set to “probable” but is under constant review, according to our own Prime Minister, Malcolm Turnbull.

Speaking on the ABC’s AM program, Turnbull explained that while that level is unchanged at this stage, people can expect to see a stronger police presences in the streets and at large public events in the coming weeks and months.

"You'll see heightened police presences at events like [Sydney's Vivid festival], you will see more obstacles, bollard, barriers put in the way to prevent vehicle-borne attacks," he said.

"We must be as agile as our enemies, we have to be more agile than our enemies ...  So, we have to learn from every incident."

Australia operates on a different system to the UK known as the National Terrorism Threat Advisory System, which has five colour-coded levels each indicating the likelihood of an attack, such as the Lindt cafe siege at the end of 2015.

The levels are Certain (Red), Expected (Orange), Probable (Yellow), Possible (Blue) and Not Expected (Green).

If a change is made, the Government will inform the public exactly why, enabling authorities, businesses, and individuals to take appropriate measures.

'Probable' means there is credible intelligence that "individuals or groups continue to possess the intent and capability to conduct a terrorist attack in Australia", the website explains.

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"The public should continue to exercise caution and report any suspicious incidents to the National Security Hotline by calling 1800 123 400. Life-threatening situations should be reported to the police by calling Triple Zero (000)"

You can watch the Prime Minister's full statement on Manchester here.

If you'd like to support the victims of the attack and their families, you can donate to the Manchester attack victims fund here.