At least 18 people were killed and dozens more injured in a stampede during a Hindu festival in India on Monday after a makeshift bridge collapsed, officials said.

A low-slung bamboo-and-rope bridge erected to help devotees reach the Ganges river gave way during the annual Chhath festival dedicated to the Hindu Sun God in the eastern Indian city of Patna. The weight of such a large number of people, as they offered prayers to the setting sun, was too much. And because power cables were strung on the bridge, the area plunged into total darkness after it collapsed, triggering the stampede as people scrambled.

Most of the casualties are thought to have been from the stampede and not the collapse, AFP reports.

“Bodies of the 18 people killed in the stampede have been sent to the hospital for autopsies,” said Jayant Kant, a police superintendent in Patna.

Ten women and eight children were among the fatalities, with more feared dead as several others were still missing. Power cuts hampered rescue efforts, city administrator Sanjay Kumar Singh said.

An estimated 400,000 Hindu devotees pay homage to 65 riverside locations across India during the festival. State authorities expected the number of worshippers to swell on Tuesday as people throng riversides to offer prayers to the rising sun.