One Nation leader Pauline Hanson has used the still-unfolding terrorist attack in London to push her campaign to end Muslim immigration to Australia.

As the latest terrorist attack in London was still unfolding on Sunday morning (AEST), the One Nation leader tweeted: "Stop Islamic immigration before it is too late."

Senator Hanson’s message was accompanied by a graphic that mimicked a "Run Hide Tell" message the Metropolitan Police earlier tweeted that advised people what to do if they found themselves caught up in the attacks.

The police message urged people to run to a place of safety, hide and turn their phones to silent, and then tell the police by calling emergency services when safe to do so.

Senator Hanson's version said: "Australia is tired of Labor, the Greens and the Liberals RUNNING their campaign that Islam is good for Australia."

“Stop Islamic Immigration before Australia hits 5% like England," the tweeted graphic showed.

Meanwhile, US President Donald Trump also took to Twitter to appeal for his controversial travel ban to be reinstated.

"We need to be smart, vigilant and tough. We need the courts to give us back our rights. We need the Travel Ban as an extra level of safety!" he tweeted.

Mr Trump’s order would bar people from six predominantly Muslim countries from entering the United States.

It continues to be blocked by the lower courts.

Senator Hanson spent the past week in a dispute with Australia's spy chief over whether there are links between Middle Eastern refugees and terrorism.

ASIO boss Duncan Lewis told Senator Hanson during a parliamentary hearing he had "absolutely no evidence to suggest there is a connection between refugees and terrorism".

Mr Lewis later said the refugee program was not the source of terrorism in Australia, rather attacks were inspired by an extremist, radicalising strain of Islam.

Senator Hanson campaigned last year on a Muslim immigration ban and no new mosques.