1976 Tangshan Earthquake

Striking at 3:42 AM while most residents slept, the Tangshan earthquake leveled 85% of the buildings in a densely populated industrial city of over one million people. The Chinese government initially refused international aid, and the true death toll was not revealed until 1988. It remains one of the deadliest earthquakes in the 20th century and led to significant reforms in Chinese earthquake preparedness and building standards.