
Sai Naung, 16, was rescued a few minutes after midnight while he was clinging on to a pillar of the bridge in Tambon Chang Moi.
The teenager said he was walking across the bridge to a flower market and he wanted to try walking on narrow strip on the edge of the bridge.
One of his arms was injured as he fell, but he managed to cling on to a pillar of the bridge amid the torrent of river water below.
A rescuer used a rope to pull up the teenager who was then rushed to Chiang Mai Hospital.