With a number of close seats set to determine who forms government, figures show informal votes will have an impact on the outcome of the federal election.

The Australian Electoral Commission (AEC) said 11 million votes were counted on polling day, with the rate of informal voting on the House of Representatives ballot paper about 5 per cent, down from 5.9 per cent in 2013.

A ballot that has not been completed properly is considered an informal vote by the AEC and not counted towards any candidate.

In the seat of Gilmore on the New South Wales south coast, about 400 votes separate Liberal and Labor, yet almost 4,000 Lower House votes in the electorate were informal and do not count.

It has been a similar story in the seat of Hindmarsh in South Australia, with the leading candidates split by about 430 votes and the informal vote count just above 3,000.

Forde in Queensland registered an informal vote just above the national average of 5 per cent for the House of Representatives.

But with the LNP and ALP candidates separated by just 149 votes in Forde, the 3,600 informal ballots in that electorate would have proved crucial if properly cast.

AEC spokesman Phil Diak said the commission would look into informal voting rates as part of its regular post-election review.

"Any vote is important in determining a seat," he said.

"We have informal votes at every federal election, but just where we are now, we've counted, for example, for the House [of Representatives], most of the ballots that were cast by electors in their home division.

"It's very much those declaration votes that will influence the outcome.

"We have 15.6 million people on the roll but we don't know what the final turnout will be there, but we do know that there are a lot of declaration votes to come."

High informal counts in knife-edge seats

As of Monday, there were 11 seats considered to be in doubt after the election.

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It is a nervous wait for Malcolm Turnbull, who will not know until the end of the week whether he has won enough seats for the Coalition to win a majority in the Lower House.

Despite the Prime Minister's confidence postal votes can secure the Coalition a majority, Insiders host and political analyst Barrie Cassidy said he could not see that happening and we were "well and truly in hung parliament territory".

In the electorate of Herbert in north Queensland, there were more than 5,000 informal ballots — or 6.57 per cent of the vote there.

On two-party preferred, just 1,084 votes separated Labor's Cathy O'Toole — who is leading — and incumbent LNP Ewen Jones.

In Cowan in Western Australia, a seat which remains on a knife edge with Labor just 959 votes in front of the sitting Liberal candidate, there have been almost 3,500 informal votes.

Rate of informal vote on Senate paper even higher

The rate of informal voting on the Senate paper was even higher than on the House of Representatives form.

The AEC said about 6 per cent of people voted informally for the Senate, up from 3 per cent at the last federal election.

The Government introduced new Senate voting regulations just prior to the ballot, with the AEC running an information campaign to help voters transition to the new way of marking the form.