Razor blades have been found in a returned same sex marriage postal survey, the Australian Bureau of Statistics says.

There have been 34 complaints of fraud relating to the postal survey, ABS deputy Australian statistician Jonathan Palmer told a Senate committee hearing in Canberra on Wednesday.

Mr Palmer said 14 of those complaints were referred to the Australian Federal Police and were related to the attempted sale of survey forms online, while another four were referred to state and territory police and involved survey form theft.

A number of the envelopes contained items which appeared suspicious, including one which had razor blades.