More than 300 possible jihadists were blocked from leaving Australia in the seven months to January — almost double the rate of the year before — amid a Government crackdown on Australians travelling to fight in Iraq or Syria.

There were 312 people pulled off planes in the seven months to the end of January, compared to 336 in the almost 12-month period before that, Immigration Minister Peter Dutton's office confirmed.

It was not clear how many of the suspected jihadists stopped from leaving were actually heading to the Middle East to fight, with some eventually allowed to resume their journey.

"In some cases, a person who was 'offloaded' may be allowed to continue with their travel plans if they are no longer considered a risk," a spokesman added in a statement.

The Federal Government has been increasingly concerned about Australians fighting with jihadist organisations, such as Islamic State in Iraq and Syria, saying some 120 Australians had left the country to join such groups.

Another 160 are actively supporting extremist organisations at home through financing and recruitment, the Government has said.

Under sweeping counter-terrorism measures aimed at blocking jihadists from going overseas, the Government introduced laws in late 2014 that would see anyone who heads to nominated areas face up to 10 years' jail.

Legislation was also passed late last year to strip duel nationals involved in terrorism of their Australian citizenship.

Iraq's second city Mosul and the IS stronghold of Raqqa in Syria have so far been added to the nominated areas list.

ABC/AFP