A nighttime biking craze has sparked a backlash from Chinese officials concerned about traffic chaos and caught off guard by a surprise mass-cycle of university students — a demographic with a history of protest.

Thousands of cyclists flooded a six-lane highway this weekend, according to videos that swept Chinese social media, as they made the 50-kilometer trip from Zhengzhou to an ancient city in central Henan.

Students overwhelmed the town of Kaifeng, with some riders dumping their rental bikes on arrival, local media reported.