Universities have been accused of "actively covering up sexual assaults" in a submission to the Australian Human Rights Commission, which alleges there have been just six expulsions in the past five years despite more than 500 official complaints.

The allegations, made by the advocacy group End Rape on Campus Australia, are based on more than five years of data and freedom-of-information requests, which show more than 500 official complaints of sexual assault and harassment have been made to universities in the past five years, with 145 reports relating specifically to rape.

In that same period 153 sexual assaults have been reported to police from the addresses of universities in NSW, the ACT, Victoria and WA. There have been six expulsions during that time.

As hundreds of thousands of students return to university on Monday, the report highlights harrowing cases of sexual assault and "hazing" at the nation's top universities, including the University of Sydney, which called in former sex discrimination commissioner Elizabeth Broderick last year to clean up the culture of its residential colleges.