Australia has closed its doors.

What next?

Nearly half of Australians say they want to ban Muslim immigration and the Treasurer, Scott Morrison, warns "it would be foolish for anyone to deny that there is concern about immigration in Australia".

But what would actually happen if Australia halted its immigration intake?

Population growth would halve

Net overseas migration – arrivals to Australia minus Australians departing – accounted for more than half of the growth in the Australian population last year. Of the 326,100 people added to the population count, just 148,900 came from so-called "natural" increases – births minus deaths.

The remainder, or 177,100, came through more people migrating here than departing. This pace of migration has actually slowed in recent years after hitting a peak of 315,700 in 2008 – the year the global financial crisis washed up on our shores. A clamp down on foreign student visas and slackening business demand for skilled migrants explains the recent fall.

Economic growth would falter

"One of the key drivers of growth in the Australian economy has been strong population growth," explains HSBC Bank's chief economist, Paul Bloxham.

Australia's quarter century of uninterrupted growth is due in no small part to a swelling population. "That makes us quite different to a lot of other countries across the world who have got the challenge of population growth that's slowing, or shrinking, like Japan."

Slower economic growth is less of a problem if what is produced has to be shared among fewer people. But migrants add to demand in the economy, helping to prop up spending and incomes, says Bloxham. "The net effect is still positive."

Our workforce would age quicker

The median age of all new arrivals to Australia last financial year was 26.5, according to Australian Bureau of Statistics. This includes temporary and permanent visa holders. The median age of the entire Australian population was 37 years.

More than two thirds of Australia's annual migrant intake arrive on skilled working visas. While family reunion visas make up a large part of the remainder, they include children as well as grandparents.

On average, new migrants lower the age profile of the Australian population and are more likely to be of working age.

The federal budget would blow out

With no new migrants arriving, there would be fewer working aged people to pay the income taxes needed to support an ageing population.

There may be some cost savings for government in helping new arrivals, particularly refugees. But Australia's annual humanitarian intake is only 13,750 a year – less than a tenth of total migration. Most migrants to Australia contribute to the workforce, given our skew towards skilled labour, and pay significant taxes.

Roads would remain crowded, housing expensive

At the margins, traffic congestion might not continue to deteriorate as quickly if immigration was halted. But there's no reason to believe it would get better.

Similarly, there would be fewer potential buyers of property. But tax incentives remain that promote excessive speculation on housing, and foreigners are still able to purchase property in Australia without actually migrating here. Furthermore, builders could simply respond to less demand by building fewer new homes.

HSBC's Bloxham says the belief that ending migration would solve all the growing pains of Australian cities is a misnomer: "We have to keep building infrastructure to keep pace with the growth in the population. The better approach here is to find a way to build good infrastructure rather than slow down our growth prospects by limiting population growth."

Education and tourism would suffer

Export revenue from international students is worth more than $20 billion a year to the Australian economy and is today our third biggest export after coal and iron ore.

Tourism also supports the jobs of nearly one million Australians. The chief executive of the Tourism & Transport Forum Australia, Margy Osmond, says halting immigration would hurt the industry.

"Particularly for the Chinese market, holidays, education and long-stay family reunions are a big reason for them to come here, stay longer and spend more in our economy," says Osmond.

Shutting the doors to New Zealanders would also hurt reunion visits from that country, which remains our biggest source of inbound tourists at 1.3 million visits a year.

"Overall, there is a tourism benefit from being perceived as an open, multicultural and welcoming country," she says

It'd be harder to find a doctor

Angela Julian-Armitage is a barrister and national president of the Migration Institute of Australia, a body representing Australia's migration lawyers and agents, who in turn represent both migrants and businesses looking to hire migrants.

Without immigration, she says: "The skilled occupation lists would never get filled. Seeing doctors and nurses would be harder for everyone. A lot of businesses would have to close. Universities would collapse without international students' income. We would have a rapidly diminishing taxation base to fund the running of the country and the ageing population, and - most of all - Australians who married a non-Australian overseas could not bring in their new spouse."

So there you have it: lower growth, a budget blowout, skills shortages and jobs put at risk. Proponents of halting migration should be careful what they wish for.