XI'AN, July 20 (Xinhua) -- More than 700 professional rescuers and over 1,500 local people are searching for 31 people who are unaccounted for after their vehicles plunged into a flooding river due to a highway bridge collapse amid torrential rains in northwest China's Shaanxi Province.

In addition, 12 people were found dead, and one person was rescued, according to a press conference held in Zhashui County, in the city of Shangluo, on Saturday.

Zhao Jing, Party chief of Shangluo, said the rainstorm triggered a flash flood on the Jinqian River in Zhashui at about 8:40 p.m. Friday, causing a 40-meter-long section of the No. 2 Bridge in Yanping Village to collapse.

The 366-meter bridge spanning the Jinqian River is a part of the Danfeng-Ningshan expressway.

Zhao said that, based on the highway toll system and video surveillance, as well as telephone inquiries, the rescuers concluded that a total of 17 cars and eight trucks had plunged into the river.

Rescuers are still searching for 18 vehicles with 31 people aboard along a 60 km stretch downstream from the collapse site, Zhao told the press.

The search operation has made use of drones and kayaks. The local authorities have been making contact with family members of the victims, and carried out measures to prevent secondary disasters, while monitoring geographical risks and fighting the flooding in the area.

Before the press conference, the participants observed a moment of silence for the victims.

The water flow of the river has now slowed to 130 cubic meters per second, with the water level dropping by more than three meters, compared with the level when the bridge collapse occurred, making the conditions conducive to the search and rescue work.

Zhao said that six rounds of heavy downpours have lashed the region since the beginning of July, increasing the risk of flooding on five major rivers, with disasters reported in seven counties and districts of the city. A total of 64,278 people have been affected. The local authorities have relocated 37,597 people due to safety concerns.