Chiang Mai officials rushed to close off the site to tourists and locals and examine the damage. The Fine Arts Department has deployed staff to aid with renovation work.
The regional Fine Arts Office said about 10 metres of the wall had toppled due to heavy rain.
Office director Therdsak Yenjura said the wall around Chang Phuak gate was last maintained about 60 years ago.
It is thought to have been built during the reign of King Mengrai of Lanna (AD1261-1292).
“The 7th Regional Office of Fine Arts will erect reinforcing pillars before conducting maintenance," Therdsak said.