The current climatic phase is significantly affecting the global cryosphere, resulted in the incipient small glacial lakes, expansion of existing glacial lake areas and volumes, a decline in permafrost coverage. This study aims to quantify glacial lake dynamics in the Lachung Basin of Sikkim, Eastern Himalaya, with a particular focus on potentially dangerous glacial lakes (PDGLs). Using satellite imagery and aerial photographs from 1974 to 2023 (area of >0.001 km²), an updated inventory of glacial lakes was compiled. In 2023, a total of 99 lakes were identified, covering an area of 4.570 ± 0.29 km². Between 1974 and 2023, both the number (from 46 to 99) and total area (from 2.986 ± 0.10 km² to 4.570 ± 0.29 km²) of glacial lakes grew substantially. A strong correlation was observed between glacial lake expansion and the accelerated rate of deglaciation from 2001 to 2014, with the highest recorded lake area expansion rate of 0.057 km²/y in this basin. The expansion rate varied by lake type, with supraglacial lakes showing the lowest rate at 0.013 km² per/y (1988–2001), while proglacial lakes expanded at a higher rate of 0.037 km²/y over the same period. The supraglacial lake at Tenbawa glacier has a history of Glacial Lake Outburst Floods (GLOFs) in 1998, and rapidly expanding afterwards, likely due to climatic changes. Furthermore, other supraglacial lakes on Illibu Khangse glacier were identified as high-risk for GLOF events. Field mapping documented an unreported breach of a small moraine-dammed lake on August 2, 2023, and later quantified through satellite imagery. To evaluate the outburst risk of PDGLs, 22 key determinants were analyzed using the Analytical Hierarchy Process (AHP), categorizing 24 identified PDGLs into three risk levels: 9 lakes were classified as very high risk, 12 as medium risk, and 3 as low risk. With nearly 88% of lakes falling into the medium to high-risk categories, urgent and precise bathymetric and geophysical assessments, permafrost evaluations and continuous monitoring, are essential for risk mitigation. It is crucial not to underestimate even small glacial lakes, as their potential breaches could lead to catastrophic cascading effects downstream.