More than 18,000 people have been asked to explain why they apparently voted more than once at the federal election.

Despite heavy fines and the risk of jail time for multiple voting, two people were marked off the electoral roll 11 times on July 2.

A further two people had their names marked off five times, while four others had four marks and 51 people had three marks.

Australian Electoral Commissioner Tom Rogers told a Senate estimates hearing on Tuesday night 18,343 people have been asked to explain why their name was checked off more than once, with many expected to be in error.