The total value of international education to the NSW economy has jumped nearly $1.5 billion since 2013, from $5.5 billion per year to $6.96 billion in 2015, NSW Department of Industry figures based on Australian Bureau of Statistics data show.

The state is now drawing about a third of Australia's total international education earnings, estimated at $21 billion per year.

The value of the sector to the NSW economy is now significantly higher than tourism, which was worth $5.2 billion in 2015.

International student numbers in NSW have increased by 22.4 per cent since 2013, growing from 140,000 enrolments in the first half of 2013 to 171,000 in the first half of 2015.

Nearly half of the international students enrolled in NSW universities are studying management and commerce courses. Society and culture courses are the next most popular, accounting for a quarter of international students. The remainder of international students are mainly enrolled in mixed field programmes, engineering and related technologies and information technology courses, according to the NSW government.

The University of Wollongong has the highest proportion of international students in NSW, where they make up more than 40 per cent of the total student population, according to the university's data.

"Attracting international students is a crucial driver to the NSW economy and education is our State's largest services export," NSW Minister for Trade Stuart Ayres said.

"A growing middle class in Asia has increased the number of students looking at NSW for their studies."

International education is now one of Australia's largest service exports and a 'super growth sector' driving the transition away from resources.

Nationally, one in five university students are international students, with more than a quarter coming from China. About a tenth of international students come from Singapore, the next biggest source country.

However, concerns have been raised by the University of Sydney and the Grattan Institute about a decline in the quality of international education.

"Many academics believe that courses are being 'dumbed down', or that it is becoming easier to pass or get high grades," a 2016 Grattan Institute report on higher education in Australia said.

This is supported by data showing a significant increase in pass rates for international students compared to a slight fall in pass rates for domestic students.

"In 2010, international commencing students were for the first time more likely to pass their subjects than were domestic students," the report said.

At the same time, international students consistently report lower average marks than domestic students, according to the Grattan Institute.

University of Sydney vice-chancellor Dr Michael Spence last month said a fall in teaching quality could be partially attributed to universities' increasing reliance on full-fee-paying international students, especially in "inexpensive subjects", to make up for losses of "$20,000 per student, per year" in other areas such as medicine with strict teaching requirements.

Dr Spence was arguing for changes to the deregulated 'demand-driven' funding system introduced in 2012, under which caps on places in a number of bachelor degrees were removed.

A spokesperson for UNSW said it has not seen a decline in "graduate outcomes" due to increasing international student numbers.

"UNSW has noted the increased attractiveness of its professional postgraduate programs to international students and has seen growth in this area in recent years," the spokesperson said.

"We have seen no reduction in student satisfaction or graduate outcomes associated with this moderate increase."