Roadblocks were set on Fung Cheung Road and Castle Peak Road, and traffic was brought to a standstill.
Protesters were also seen throwing petrol bombs at police cars. Meanwhile on one occasion, a passerby was attacked by demonstrators after getting into a quarrel.
In a warning issued by the police, they said a large number of protesters are in the vicinity of Yuen Long West Rail Station.
“Some even threw petrol bombs to police vehicle, causing danger to the life of the police officers onboard,” the statement said.
Earlier, protesters also vandalised the bridge linking the Yoho Mall to the Yuen Long MTR station by throwing buckets of sand and spray-painting the MTR gate.
The mall then started making broadcast announcements about an “emergency situation”, asking people to leave for safety reasons.
Hundred of police officers, dressed in riot gear, are now on standby in the Yuen Long area.