An ultrasound system comprises an ultrasound unit including: an ultrasound probe including a first set of imaging transducer elements and a second set of localisation transducer elements. The first set of imaging transducer elements are configured to: (i) produce ultrasound imaging transmissions into the human body, wherein the ultrasound imaging transmissions are focussed into an image scan plane, and (ii) receive reflections of the ultrasound imaging transmissions for generating a two-dimensional anatomical image corresponding to the image scan plane. The second set of localisation transducer elements are configured to produce ultrasound localisation transmissions into the human body for locating the medical instrument with respect to the anatomical image, wherein the ultrasound localisation transmissions extend outside the image scan plane.