<p>Heatwaves have become more frequent and intense under anthropogenic climate change, with profound implications for both natural ecosystems and human systems. However, the transboundary migration of heatwaves over China remains unclear, overlooking the significant influence of exogenous heatwaves—those originating outside the region—hampers accurate predictions and effective mitigation strategies to deadly heatwaves. Here we assess the impacts of exogenous heatwaves on heat risks across China using a Lagrangian tracking approach. Surprisingly, our results reveal that 42.7% of heatwaves in China are linked to exogenous heatwaves. These external extreme heat events have shown a marked increase (4.35 events/decade), affecting the entire country, especially the northwest, northeast, and southeastern coastal regions. China experiences approximately 3.49 days of exogenous heatwave exposure per year, with an upward trend of 1.42 days/decade. Anthropogenic climate change emerges as the primary driver behind the intensification and increasing exogenous heatwaves. Future projections suggest that exogenous heatwaves will worsen and become the dominant type. At the 1.5 °C global warming level under the SSP585 scenario, exposure to exogenous heatwaves is projected to increase by 236.3%, frequency by 188.3%, cumulative heat by 313.4%, and the affected area by 98.5% compared to historical baseline. Limiting global warming to 0.5 °C could prevent 28.7% of exogenous heatwave exposure, 39.8% of population exposure, and 31.3% of economic losses in China. This study underscores the critical role of exogenous heatwaves in amplifying regional heatwave impacts, highlighting the need for targeted mitigation efforts to address this growing deadly threat.</p>