Migrants who arrived in Australia five years before Census 2016 are not speaking English as well as those who'd lived in the country for the same period in 2011.
There has been an almost two per cent decline in English proficiency among migrants who've been in the country for five years, compared to six years ago for those who'd lived here for the same period, Census 2016 reveals.
In 2011, some eight per cent of the migrant population who had been in the country for five years could not speak English well or not at all.
But in 2016, that figure had risen by 1.8 per cent.
About 9.8 per cent of the migrant population who had arrived five years before (in 2011) could not speak English well or not at all.
Dr Anna Boucher, who studies migration and public policy at the University of Sydney, says Australia now takes migrants from a greater range of countries and more are "coming from China and India".
In 2010-11, for the first time in the history of Australia, China surpassed the UK as Australia's primary source of permanent migrants.
And by 2011-12, India was the largest source country at 29,018 places (or 15.7 per cent) of the total migration program, followed by China (25,509) and the UK (25,274).
Of that, the top 10 source countries for skilled migration visas were India (nearly 25 per cent of the population), China (16.4 per cent), followed by the UK (13.4 per cent), Sri Lanka, Malaysia, South Africa, the Philippines, Nepal, Iran and South Korea.
In contrast, in 2006 most of Australia's migrants were born in the UK, accounting for 23 per cent, followed by New Zealand (10 per cent) and Italy, China and Vietnam (four per cent each).
Dr Boucher said the increase in migrants who say they don't speak English well is partly because the "bulk of migrants are not subject, even coming through the economic (visa) stream, to selection criteria".
She adds it may also be because "skilled migrants speak English at quite a high level, but their spouses, kids and grandparents do not".
However, "if you give them the opportunity to take an English test and have their skills accredited prior to their arrival, then they're more likely to do well".
Proposed changes to Australia's citizenship laws, including a more stringent English test, are currently before parliament.
Labor MP Tony Burke on Sunday lambasted the proposals in an interview with ABC TV after citing an alleged extract of the test that referred to Greek historian Herodotus, who lived in the 5th Century BC, and the Battle of Thermopylae.
"There is not a single person in Australia who would have to say you would have to do a comprehension test like that before you can pledge allegiance to this country," Mr Burke said.
However Immigration Minister Peter Dutton defended his government's planned crackdown.
"The citizenship legislation requires those seeking Australian citizenship to be competent in English. Competent equates to Level 6 of the International English Language Testing System [IELTS]," he said in a statement last week.
There are two streams to IELTS – academic and general training.
"Contrary to Labor's false claims, the IELTS academic test is not required for migration or citizenship purposes. The general training test is accepted," he said.
Dr Boucher adds that while Australia increased its humanitarian intake from 13,017 in 2006-2007 to 17,555 in 2015-2016, this was a "blip" in Australia's total migrant population of 182,165 between 2015-2016.
Professor John Hajek from the University of Melbourne told SBS World News another reason why more migrants now have less command of the national language is because of family reunions.
The 2016 Census shows the average European-born migrant is 59 years old and the average Asian-born is 35.
The average 35-year-old Asian resident is "exactly the age ... that's going to be targeted for reunions," he says, adding their parents are "less likely to pick up English because they're more likely to be at home" or in their cultural communities.
In the 2011 Census, 24.3 per cent of 55-64 year old migrants who'd lived in the country for five years lacked English proficiency.
This was at 30.4 per cent for the 65-74 age bracket, 35.1 per cent for 75-84 year olds and 31.2 per cent for 85 and older.
In the 2016 Census, lack of proficiency had grown to 40 per cent of 55 to 64 year-old migrants, 47 per cent for 65-74 year olds, 51 per cent for 75-84 year olds and 46.3 per cent for those over 85.
In September last year, the topic of parent visas was hotly debated when the Productivity Commission released a report suggesting parents of migrants cost the country too much at between $2.6 billion and $3.2 billion over their lifetimes.
The Australian Government announced a week later it was developing a five-year temporary, continuous visa for parents of immigrants, set to take effect on July 1 2017.
Assistant Immigration Minister Alex Hawke said at the time: "Reuniting three generations of families has great societal benefits, and that's why we're announcing a temporary visa of five years."
Younger people show greater command
In 2011, 1.9 per cent in the 0-14 age bracket could not speak English well, 3.6 percent in the 15-24 bracket, 6.3 per cent in the 25-34 age group, 10.4 per cent in the 35-44 range and 15 per cent in the 45-54 bracket.
In 2016, 1.7 per cent of 0-14 year olds did not have good command of the language, 4.2 per cent in the 15-24 year range, 7.3 per cent between 25-34 year olds, 10.2 per cent for 35-44 year olds and 21 per cent in the 45-54 age group.