Australia upgrades travel advice to UK due to 'threat of terrorism'

Australia has upgraded its advice for travellers to the United Kingdom due to the "threat of terrorism".

The government's SmartTraveller website says Aussies should now "exercise a high degree of caution in the UK" due to the threat.

The warning level has moved from green to yellow, alongside nations such as the USA, Peru, France, Greece and Indonesia.

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Green is level one which means people should exercise normal safety precautions like using common sense and looking out for suspicious behaviour.

Yellow is level two which means exercising a high degree of caution and urges people to pay close attention to their personal security and the current health situation.

Orange, level three, warns travel should be reconsidered and to avoid non-essential travel.

Red, level four, advises people not to travel to that country.

"International terrorists have staged attacks in the UK," the SmartTraveller website said.

"The UK Government's terrorism threat level is 'substantial', meaning it assesses an attack is likely.

"Islamic extremism, extreme right-wing ideology and the status of Northern Ireland contribute to the threat."

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There are five threat levels in the UK and "substantial" is the third highest.

Authorities warned travellers to always be alert to the threat of terrorism and to take official warnings seriously.