On an excursion trip to Himachal Pradesh, 24 students from Hyderabad are feared to have been washed away by the Beas on Sunday after a hydropower plant allegedly discharged water into the river without any warning, triggering protests by local residents.
The incident took place in Thalaut on Manali-Kiratpur Highway, 40km from district headquarters Mandi. A massive search operation was launched to track the students, but there was no success due to darkness.
Six girls are among the missing, many of whom are in their late teens.
It is learnt that altogether 38 students from VNR Vignana Jyothi Institute of Engineering and Technology, Hyderabad, were on the riverbank when the water level rose after discharge from a reservoir of the 126 MW Larji hydel power project around 2km away.
"The students had stopped to take photographs on the edge of the Beas at 7.30pm when water released from a dam washed them downstream," Himachal Pradesh transport minister GS Bali said.
The students were travelling to the resort town of Manali further north.
Enraged residents of Thalaut and surrounding areas blocked the national highway after the incident, accusing the hydropower project authority of releasing the water without warning.
Rescue workers using torches in the dark were attempting to find the students in Kullu Valley, some 200km north of state capital Shimla, Bali said.
The services of divers have been requisitioned for rescue efforts.
People living along the two sides of the riverbank downstream of the dam were alerted to inform the police about any person sighted by them.
The incident sent shock waves, and parents and friends of the missing students made frantic calls to know about their whereabouts.
As time elapsed and rescue efforts continued without success, fears rose that some of the students might have drowned.
"I am deeply pained over the tragic incident of engineering students getting drowned in a flash flood in Himachal Pradesh," home minister Rajnath Singh said on his official Twitter account.
"I have instructed the authorities to despatch a rescue team for immediate action and save precious lives trapped in the floods," he said in a tweet.
A local official blamed the surge of water on the hydroelectric power plant for the tragedy.
"The water was released by the Larji power project dam," AFP quoted senior state official Rakesh Kanwar as saying.
The Kullu Valley is home to raging rivers, dense forests and steep gorges.
Himachal Pradesh and other Himalayan states, including neighbouring Uttarakhand, are home to a string of hydroelectric projects as India rushes to expand power generation to meet the rising demand.
Governments are attempting to harness the power of rivers despite the risk of environmental damage to diversify away from costly and polluting coal and gas plants to meet the country's electricity shortage.
(With AFP and PTI inputs)