Not enough Australians are voting and not enough young people have enrolled to vote, latest figures show.

Statistics from the Australian Electoral Commission (AEC) revealed 20 per cent of eligible voters did not cast their ballot in the last federal election and 25 per cent of young voters failed to enrol for the next election.

Of those aged 18-24, 400,000 people did not enrol in time meaning they cannot vote in September's election, a trend that is of great concern to the AEC.

"It is clear from the evidence that the trend is for increasing numbers of otherwise eligible electors to remain outside the electoral system," Electoral commissioner Ed Killesteyn said.

The AEC studied the 2010 election and found more than 3 million Australians did not vote.

Of those 1.5 million people were not enrolled, 900,000 people were enrolled but did not vote and nearly 750,0000 people cast an informal vote.

An informal vote is a ballot paper which has been incorrectly completed or not filled in at all.

The AEC says not all non-voters were doing so deliberately nor were all informal voters doing so on purpose.

Attempts to boost voter numbers have been made by encouraging online enrolments.

"Encouraging all eligible Australians to enrol to vote will continue to be a priority for the AEC at future elections, as will providing voter information and support services to those Australian who are under-represented in our electoral system," Mr Killesteyn said.

Young voters are 'not engaged or interested'

Associate Professor Joo-cheong Tham, an expert in Australian electoral law at the University of Melbourne Law School, says the figures mean one-in-five Australians are not voting and that leads to a "democratic deficit".

Professor Joo-Cheong Tham says many young voters are not engaged or interested in the electoral process.

"One-in-five are not voting, that is a serious issue, a serious democratic deficit," he said.

"It is concentrated among the young. We are talking about people coming into the political process, reaching adulthood who are for one reason or another disengaged from politics.

"These are a set of issues that at the very least deserve serious consideration. There should be much more public concern about that."

"I think it feeds into the aspect that the spirit of democracy is not as lively in this country as it should be."