Two Explosions Go Off At Brussels Airport, Third Explosion At Train Station

Prime Minister Malcolm Turnbull said Australia's terror threat level would remain unchanged in the wake of the attacks on Brussels, saying our airport measures and borders were stronger than Europe's.

Turnbull conducted a series of interviews on Wednesday morning, condemning as “cowardly” the terrorist attacks in Brussels which killed at least 34 people overnight.

Turnbull told ABC News 24 while Australia's security measures were sufficient, the nation needed to remain "constantly vigilant".

"We are in a stronger position from a security point of view than the Europeans are. As you know, there are -- for all intents and purposes -- no internal borders [in Australia]. We have strong border protection.

"We have a much greater insight into people who we would regard as being threats or likely to pose a risk to safety of Australians.

"While we obviously cannot guarantee that there will not be terrorist incidents in Australia and that's why the threat level is probable and has been so for 18 months, nonetheless, we have very strong measures in place.

"The more we learn about the techniques and methods of these murderous terrorists the better we are able to protect Australians."

Turnbull confirmed Australia’s long-running solidarity with Belgium, forged during WWI.

“Our thoughts, our prayers and our most resolute solidarity are with the people of Belgium,” Turnbull said in Canberra this morning.

“We are totally united in the fight against terror and the people of Belgium know we stand with them just as our forebears stood with the people of Belgium 100 years ago.

“We are in a battle with these terrorists and we will defeat them.”

Foreign Minister Julie Bishop, who is presently visiting Indonesia, said she had spoken to Australia's ambassador Dr Mark Higgie to ensure staff and their families there were safe.

She condemned the attacks and said Australia's thoughts and prayers were with Belgium.

The Department of Foreign Affairs and Trade was actively trying to find out whether any Australians had been caught up in the blast, although no reports had been received by Wednesday morning.

Travel advice has been upgraded, with Australians encouraged to "reconsider" their need to travel.

This is based on not just the security uncertainty in the aftermath of the attacks, but that public transport has been shut down and flights in and out of Brussels cancelled.

"Australians in Belgium should remain attentive to their surroundings, avoid affected areas and follow the instructions of local authorities," the update states. Australians currently in Belgium can find more advice on the Smart Traveller website.

Those seeking to contact family or friends in the region have been asked to try to contact them first, and then call DFAT's hotline.

Airports across Europe -- including Paris, Frankfurt, Sweden, Finland, Denmark and London -- have upgraded their security since the Brussels explosions.

France also has an additional 1,600 police to provide additional security at their airports and other transport hubs. Flights from France and Belgium and direct trains between Paris and Brussels have been stopped.

Brussels remains in complete lockdown following three explosions at the Belgian capital's Zaventum airport and a metro station, which have claimed the lives of at least 34 people and injured dozens more.

In the first attack at Zaventum international airport on Tuesday night (AEST), an explosion at least 14 people. A short time later, a third explosion at Maalbeek metro station caught people on their way to work at around 8am local time.

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