Northern Territory Police are calling for witnesses to an alleged sexual assault on Smith Street, Darwin City about 6:15pm Wednesday.

The incident happened near Edmunds Street.

Information suggests a passer-by intervened sometime during the assault.

Police would like this Good Samaritan – or anyone else with any information – to contact police on 131 444 or Crime Stoppers on 1800 333 000.

A 40-year-old man has since been arrested and charged with sexual intercourse without consent and gross indecency in a public place.

He will appear in Darwin Local Court today.