Desiree Sheets-Chavolla works as a cleaner at Sydney Airport.

She currently does an average of 26 hours a week but would like to work more.

"I'm constantly having to ask for extra work," she told 7.30.

"They've created like a shark tank for us — we have to fight for any overtime."

Ms Sheets-Chavolla is not alone. Exclusive market research for 7.30 shows almost 1.2 million people were underemployed last year and the problem is only predicted to get worse.

Women, the young and hospitality and retail staff most likely to be underemployed

Michele Levine says part-time jobs are growing at a faster rate than full-time work. ( ABC News )

Roy Morgan Research analysed 15 years of research and found the number of underemployed people had jumped almost 450,000 since 2005.

The research is based on thousands of face-to-face interviews conducted across the country each month.

CEO Michele Levine said an increasing number of workers were frustrated about being trapped in part-time work.

"Essentially what they're saying is they've got a part-time job, but they would really like to be working more hours," she told 7.30.

"Part-time jobs are growing at a faster rate than full-time jobs. And clearly, when you have part-time jobs, you have a lot of those people would prefer to have more work, they'd prefer to have a full-time job."

According to the Roy Morgan research, 8.7 per cent of the workforce is underemployed, slightly higher than the Australian Bureau of Statistics' (ABS) official figure of 8.5 per cent.

And you are more likely to be underemployed if you are a woman, a worker in your teens or 20s, or you work in three industries where part-time work is common.

The recreation and personal sector, which includes hospitality and fitness workers, is the industry with the highest underemployment, at 20 per cent, followed closely by retail with over 19 per cent underemployment, and community services, which includes teachers and carers, at 10.5 per cent.

'You're always waiting for the next payday'

Despite working two jobs, Desiree Sheets-Chavolla is still struggling. ( ABC News )

For Ms Sheets-Chavolla, the lack of work makes it difficult to make ends meet.

"I struggle to pay my bills, I struggle to pay my mortgage," she said.

That means she puts off fixing essentials like her broken hot water heater which is leaking water.

Despite a 50-kilometre commute to the airport for shifts as short as four hours, Ms Sheets-Chavolla has taken on a second cleaning job but says it isn't enough to fill the financial shortfall.

"It doesn't come easy because you're always robbing from Peter to pay Paul and you're always waiting for that next payday and its very stressful," she said.

Roy Morgan's Ms Levine said the economy would benefit from people having extra work if they wanted it.

"We're under-utilising the potential of our people to be doing meaningful work," she said.

"That in itself is a bad thing, that holds the economy back.

"If more people were actually working and working as many hours as they wanted to, they'd have more money to spend, and that of course, feeds the economy."

The ABS uses a strict definition to calculate its unemployment and underemployment statistics so that it can compare Australia's results with that of other countries.

A person is counted as being employed if they work one hour a week.

$50 for a three-hour shift — 'It's just not enough'

Ndonde Fikiri is looking for extra work, without much luck. ( ABC News: Chris Gillette )

Ndonde Fikiri enjoys her part-time in retail but she wants to work more.

Her shifts can be as short as three hours.

"A three-hour shift, that's like barely $50," she told 7.30.

"Sometimes it takes about $6 to go and come back from work. It's just not enough."

She has been going door-to-door to retail outlets, handing out her resume in a search for more work.

She's not having much luck.

"Only one of the retailers accepted my resume," she said.

"[The search] continues."

Ms Fikiri is trying to save enough to pay for a business degree at university.

"I have to pay for my own uni, and I just can't sit around and wait, getting three-hour shifts per day."

"How am I ever going to pay $4,000 a semester? I need a job."

More people working part-time

Jeff Borland thinks the problem of underemployment will continue to get worse. ( ABC News )

According to Jeff Borland, a professor of economics at the University of Melbourne, there has been a significant shift to part-time work over decades, which is causing the spike in underemployment.

"Underemployment really is a part-time work phenomenon," he told 7.30.

"Back in the mid-1960s, for example, only about 10 per cent of jobs were part-time then and the rate of underemployment was 1 per cent.

"So, only one in 100 workers in the labour force then said that they were underemployed.

"Nowadays with part-time employment, it's about a third of the labour force."

He said even the well-educated were finding it harder to land full-time work.

"Whereas 10-15 years ago, if you had a degree and wanted a full-time job, you're pretty likely to get that straight away, now it's about a quarter of people who get a graduate degree, three months after they graduate are doing part-time work, and it's taking them several years to get the full-time job they want."

Professor Borland predicts underemployment is likely to get worse, particularly after hits to the economy from this summer's bushfire and the coronavirus outbreak.

He said the Morrison Government should look at budget stimulus to try and combat the issue.

"The signs are that part-time employment will continue to grow," he said.

"If you extrapolate past trends and taking account of the likelihood of some weakening in the Australian economy, it is quite likely that underemployment will continue to rise."

For airport worker Desiree Sheets-Chavolla, underemployment is a worrying trend that makes her worry about the future for her children.

"It's grim. You know, it's sad to see that that's where this world is going," she said.

"We want to make it better in the future.

"We want people to have full-time jobs and it's just not going that way."