Posts on Twitter and China's Weibo social network described a chaotic scene and rescue efforts along the Shanghai riverfront.

Photos showed large crowds packing a street near the river and emergency medical workers treating people on the ground.

The stampede broke out around 11:35 p.m. Wednesday along the city's riverfront, the state-run Xinhua news agency said. At least 42 people were injured, Xinhua reported.

Authorities are investigating the cause, Xinhua said.

A witness told the government-run news agency that people started scrambling after coupons that looked like dollar bills were thrown from the third floor of a building.

Many of the dead were young students, CCTV America reported, citing Shanghai rescue authorities.

Video from the Reuters news agency showed people sobbing in a hospital waiting room. One woman told CCTV they'd been waiting for hours for information about their loved ones.

The promenade in the area known as the Bund along the Huangpu River is a popular spot for New Year's Eve festivities in Shanghai.

But last week, Shanghai Daily reported that local officials had called off a popular New Year's Eve light show there, citing police concerns over crowd control. Last year, the event drew nearly 300,000 people and "dispersing the crowd became a massive administrative headache," the newspaper said.

Scaled-back celebrations had been planned in several parts of the city instead, according to the newspaper.

Officials canceled another New Year's celebration late Wednesday in front of Beijing's tallest skyscraper, citing safety concerns.

Even with the light show and official countdown called off, many revelers remained at the location and had their own countdown there.

(CNN)