The lantern and fireworks display ended in disaster on Thursday when spectators packed on a metal bridge died in the crush, a doctor said.
"Most of them were crushed and suffocated by the crowd," said a doctor at the county hospital in the Beijing suburb of Miyun.
The bridge, bedecked with red lanterns, spans a 100-metre canal.
Nearly 20 ambulances with sirens wailing were seen speeding up a highway in direction of Miyun. Roads leading to the area were dotted with police cars.
Witnesses said the accident happened in Mihong Park where frantic parents searched for their children in the freezing night.
"There were all these people crowding on the bridge, probably a few hundred. With that many people, there was sure to be a problem. The railing also seemed low," said witness Chi Zhangfeng.
"I heard lots of people screaming, it seemed like it happened pretty fast," he said.
Officials had earlier told of a bridge collapse injuring several people, with fatalities unknown.
Chinese set off fireworks, display lanterns and eat sweet dumplings for the Lantern Festival, which falls on the 15th day of the first lunar month.