Australians travelling to France and Belgium have been told to exercise a "high degree of caution" with authorities upping the travel warning after the Paris terrorist attacks and Belgium arrests.

The new warning puts the Western European countries on the same travel security footing as countries like Angola, Bolivia, South Africa and Jamaica and comes one week after the Paris terrorist attacks.

It is highest security threat warning issued for a Western European country since the four-tier advice system was introduced in 2011.

The Department of Foreign Affairs and Trade has issued the warning saying travellers should research specific threats and the political and security situation before travelling. It says travellers should pay close attention to their personal security if they intend to travel to either country.

"Importantly, we are not saying "don't go" to this location. Rather, you should research specific threats and take extra precautions," its Smart Traveller warning states.

The Australian warning comes as Belgium's national crisis centre raised the security warning for its capital Brussels to its highest possible level saying there was a "serious" and "imminent threat".

Authorities have urged citizens to avoid crowded areas such as concerts and transport hubs in Brussels. The capital is home to the European Union and NATO headquarters.

The Australian and Belgian warnings came amid a 12-day nationwide state of emergency declared for France following the terrorist attacks that killed at least 130 people and injured more than 300 people in Paris on November 13. Islamic State has claimed responsibility for the attacks.

It also cited the terrorist attack on magazine Charlie Hebdo in January and a factory attack near Lyon for the heightened security warning.

"We assess there is a heightened threat of terrorist attack in a number of European countries, including France. This heightened risk exists across the whole of France, including Paris and Ile de France region," the travel warning statement said.

Smart Traveller also warned Australians that France had issued its highest level "Alerte​ – Attentat​". Heightened security measures remain in effect in public places, including shopping areas, tourist sites and transportation hubs. It warns people in France to be vigilant in public places and to report any suspicious activity to police.

It warned that under French law all people are required to carry photographic identification at all times. French police are conducting random identity checks, particularly at border crossings.

Belgian investigators have charged a third unnamed suspect with involvement in terrorism over last week's Paris attacks.

AAP is reporting Belgian authorities would not release further details about the "imminent threat" warning saying it would "allow ongoing judicial investigations to follow their course".

The Australian warning for Belgium is the result of the Brussels terror raids and the arrest of several suspected militants. Also, in August, a terrorist boarded the Thalys Brussels-Paris train, attacking and injuring three people on the train and the terrorist attack on the Jewish Museum in Brussels in May last year.

Around the world, tributes are continuing to those who suffered during the attacks by the so-called Islamic State in Paris.

Soccer teams have observed a minute's silence in Edinburgh and light tributes have continued the form around the world.

Buildings continue to fly the tricolour flag of France.

Music fans have felt the sadness after the attack included Eagles of Death Metal concert.

Others remain undeterred by the attacks, saying they will return to Paris regardless of warnings.