A spokesman for Sussex Police said the incident occurred shortly after midnight in Avon Close, Sompting.
Specialist officers are currently with the victim, said police.
Officers are in the area conducting house-to-house enquiries, said the spokesman, and seeking to secure any CCTV footage that may assist them.
Police said: "The investigation is still at an early stage and further information will be given as it progresses.
"Anyone who may have information is asked to contact Sussex Police online (https://www.sussex.police.uk/contact/af/contact-us/us/contact-us/provide-more-information-to-be-added-to-a-crime-report/ ) or phone 101, quoting serial 58 of 06/02.
"Alternatively please contact the independent charity Crimestoppers anonymously via its website, www.crimestoppers-uk.org, or by phoning 0800 555 111."