Under continued warming, heatwaves increasingly evolve as regional processes that persist, expand, and migrate across space. Using ERA5-Land daily maximum temperature data, we identified spatiotemporally contiguous heatwave events over mainland China during May–September of 1986–2024 and quantified their persistence, severity, affected area, and mobility. The study period was divided into three phases according to changes in annual mean daily maximum temperature: 1986–1998, 1999–2011, and 2012–2024. A total of 609 events were identified, including 177, 219, and 213 events in the three phases, respectively. Although event number did not continue to increase after 2012, event characteristics intensified markedly. During 2012–2024, the fitted rates of change in duration, cumulative severity, affected area, and track length reached 0.264 days yr^−1, 2.6 × 10⁶ °C days km² yr^−1, 1.0 × 10⁵ km² yr^−1, and 116.06 km yr^−1, respectively. Track length was significantly correlated with duration, severity, and affected area, and these relationships were strongest after 2012. The results indicate that recent heatwave hazards in mainland China are characterized mainly by stronger contiguous event processes rather than by more frequent events.