Electrical and Mechanical Services Department (EMSD) is walking through a digitalisation journey from Building Information Modelling (BIM) to BIM-Asset Management (BIM-AM) in realising digital twin for smart building Operation and Maintenance (O&M). Since 2015, the EMSD has been developing its own BIM-AM System to extend the use of BIM for O&M operations. In 2019, the EMSD established a dedicated Internet of Things (IoT) network, namely, the Government-Wide IoT Network (GWIN) and the Regional Digital Control Centre (RDCC), to support digitalisation and near real-time monitoring of Electrical & Mechanical (E&M) assets. Furthermore, the EMSD has commenced a government-wide asset digitalisation exercise in revitalising the E&M asset information of over 450 existing government venues towards smart buildings since September 2020. The on-premises Common Data Environment (CDE) conforming to ISO19650, is being established to support the adoption of BIM-AM and conclude our practice and requirement in the form of a standard and guideline for sharing to the public and released the latest version on Sept 2022. EMSD is currently exploring the possibilities of OpenBIM and other emerging technologies for information sharing and building insights. In this paper, the adoption of these smart techniques will be presented to demonstrate the realisation of digital twins in smart building O&M and facility management applications.