The federal government will spend up to $400 million in extra funds to create a dedicated new border enforcement agency, to start operating from July 1.

It's understood the new Australian Border Force agency will comprise between 5500 to 6000 officers within a couple of years, mainly armed, and potentially hundreds of new staff to be hired.

The extra funding means that the immigration portfolio will be the only one other than Defence to receive a boost, government sources said.

Immigration Minister Peter Dutton will lead the major reorganisation, but it is the fulfilment of a plan launched last year by the former minister, Scott Morrison.

The overarching idea is to gear up for bigger flows of people and goods in and out of Australia but with more rigorous enforcement in a so-called "once in a generation" overhaul.

While the number of bureaucratic staff in the departments has fallen, the federal government has been advertising for new officers to join the Australian Border Force.

The boost comes after the last budget allocated $711 million over six years to the creation and sustainment of the Border Force.

Another $150 million out of the $630 million announced last August for the national counter-terrorism package was allocated to eight counter-terrorism teams now operating at eight major airports around the country, and to the roll-out of Smartgate passport technology for international travellers.

Many of the officers will be armed and the officers will, among others things, take over Australia's immigration detention network while also taking up positions on the frontline at airports, shipping terminals and at sea, while playing a role in the gathering of intelligence and detaining offenders.

A new website, Border.gov.au, will also be launched to replace the websites for the formerly separate Immigration and Customs departments.

Last year's budget predicted there would be about 13,800 staff in the merged Immigration and Customs departments, down from about 14,300. The merger was forecast to cost about $480 million and 480 jobs across the two agencies.

But the government also claimed a saving of up to $2.5 billion over five years as a dividend from "stopping the boats" in the budget, too.

This year, the government has already flagged a saving of $168 million over four years in the Immigration portfolio.

Lessons have been learned from a failed experiment in Britain that saw an attempt to put the administrative and enforcement wings of that country's border agency into one agency.

In contrast, the newly merged agency will see the see administrative functions of the two departments merged into one. Border Force's first commissioner is expected to be the current chief executive officer of the Australian Customs and Border Protection Service, Roman Quaedvlieg.

In a major speech on the future of the merged agencies in April, Immigration Department secretary Michael Pezzullo said the focus of the new department would be to "manage a system of border processes by which we will oversee the flow of people, and goods, to and from our nation".

"Our staff will, where necessary, be expected to say 'no' more often than they do now, where circumstances warrant and within the law, as a result of the better use that they will make of new intelligence systems and other capabilities, as well as improved relationships with law enforcement and intelligence agencies, and better training and support to make defensible adverse decisions," he said.

"This is not to say that the shutters are coming down – far from it. The overall flow of visitors and migrants will only continue to increase.

"What we will focus on in the months and years ahead is the quality of our decisions in favour of the rights of the community, while still delivering the economic and social benefits of immigration.

"The Australian community right expects us to deliver those benefits, and to keep the public safe. This is not a choice. It has to be done simultaneously and seamlessly."