The arrival of high-speed rail (HSR) generates new economic opportunities and shapes the spatial distribution of economic activities and territorial dynamism. While extensive research examines inter-city phenomena, limited research focuses on intra-city dynamism, particularly how HSR affects new firm formation and their spatial distribution within a city. This paper develops an analytical framework utilising difference-in-difference methods and temporal dynamics to examine new firm registration data in Suzhou, a non-central prefecture-level city in China. The empirical evidence substantiates four key points: First, HSR significantly accelerates new firm formation. Second, there is a time lag in new firm formation; construction firms respond first to HSR services, but the most substantial responses come from the Knowledge Intensive Services and Commerce, Transport and Hospitality Services sectors. Third, there is distinct locational heterogeneity. The most developed urban districts, with their proximity to HSR stations, experience a more pronounced impact on economic clustering in the short term compared to the newly developed areas surrounding peripheral HSR stations. This study provides valuable insights for integrated transport and urban planning strategies and economic development policies by leveraging HSR accessibility to enhance intra-city dynamism.