Two passenger buses plunged into a fast-flowing river when a bridge collapsed after two days of heavy rain in a mountainous part of China, authorities said today.

An unknown number of other vehicles and pedestrians were believed to have been crossing the Tongkou River when the bridge gave way in the city of Jiangyou in the western province of Sichuan.

Officials said rescue work was under way, but there was no immediate word on casualties.

The two-lane Qinglian Bridge was built in 1967 and a replacement span is under construction.

China has been pouring resources into building infrastructure, but many older bridges and dams are of poor quality and urgently need repairs or replacement.