BEIJING — A landslide of dirt and construction debris that killed 73 people in the city of Shenzhen in December was caused by negligence and the improper storage of waste at a huge dump site, the Chinese government has concluded after a seven-month investigation.

China’s powerful State Council, which conducted the inquiry, said on Friday night that 53 people had been detained in connection with the disaster, including company executives and government officials, and that 57 others faced disciplinary measures, such as demotion.

The council also said the license of the private company managing the landfill site, Shenzhen Yixianglong, should be revoked.