A user interface comprises: a nasal cannula including one or a pair of nasal prongs configured to deliver breathing gases to a user's nares； a mask body arranged about the nasal cannula； a seal coupled to the mask body and configured to seal with an intended user's face to allow the mask body to be pressurised； a breathing gas inlet through the mask body coupled to the nasal cannula； a gas outlet from the mask configured to exhaust expired gases； and headgear coupled to the mask to retain the interface in position on a user's head, wherein the mask is configured to receive a supply of gases to a mask cavity of the mask body, in addition to through the nasal prongs. A method of supplying breathing gas to a user using the user interface includes the steps of: providing a high flow of heated and humidified breathing gases directly to the user's nares via the or each nasal prong, providing a sealed pressurised space about the user's nose, and regulating the flow rate of gases supplied to the user's nares or the pressure within the mask.
