A bridge across the Jinsha River in Sichuan province collapsed early on Wednesday after water was discharged from a barrier lake formed upstream by landslides, Sichuan Traffic Radio reported.
The collapse, which occurred in the Garze Tibetan autonomous prefecture, led to traffic jams on a major highway connecting Sichuan and the Tibet autonomous region, according to the report citing local authorities.
Traffic is unlikely to be restored soon, and drivers heading to Tibet should find an alternative route, STR said.
The flood control authority in Lijiang, Yunnan province, issued the highest level of emergency response on Wednesday morning to alert people of the potential dangers.
Water began discharging from the barrier lake through a man-made floodway on Monday.
Since it formed on Oct 11, the lake has retained about 524 million cubic meters of water, according to the Ministry of Emergency Management. It formed on the border of Sichuan and Tibet when two landslides - one in Chamdo, Tibet, and the other in Garze - blocked the Jinsha River.
Some 34,200 people were evacuated along the river as the lake's water level continued to rise, the ministry said on Sunday.