"Europe has for all intents and purposes no internal borders, so people can travel within Europe as they wish, and their external borders have been very porous - as we've been seeing every night on the news. So Europe has a security challenge or a security problem that is different to Australia. We're assisted by our geography, of course, but we also have very strong border protection that our government has maintained."

Prime Minister Malcolm Turnbull says security standards in Europe have 'slipped'. Credit:Martin Meissner

The bomb blasts at Brussels' airport and a railway station come four months after a series of co-ordinated terror attacks in Paris, killing 130 people and setting in train a manhunt that has frequently led authorities into Belgium. Salah Abdeslam, a key suspect in those attacks, is a Belgian-born French national who was arrested in Brussels last week.

The Prime Minister said that while Australia's border protection measures helped identify and repel threats to national security, there was no guarantee we could avoid similar atrocities.

"We have a much greater insight into people who we would regard as being threats or likely to pose a risk ... than the Europeans do," Mr Turnbull said. "We obviously cannot guarantee that there will not be terrorist incidents in Australia - that's why the threat level is 'probable' - nevertheless we have very strong measures in place."